Delete code relating to SQL init and scheduling (#1661)

One of the more significant changes introduced in this PR is that we use
SQL as the backing database in all tests unless otherwise specified,
e.g. by using the TmOverrideExtension. We change various ofy-related
tests to use this.

This includes various changes:
- Deletion of SqlEntity/DatastoreEntity and related classes. Includes
  any necessary changes because of that (e.g. getting a nice SQL key on
  error in RegistryJpaIO).
- Deletion of classes that used libraries from the init-sql code
  (RefreshDnsOnHostRenameAction)
- Removal of the JpaTransactionManager's backup implementation
- Modification of RegistryJpaWriteTest to not use init-sql code
- Removal of the Transaction class and related classes, however it does
  not remove the TransactionEntity class as that would require DB
  changes
- Removal of anything related to the actual usage of the database
  migration schedule or read-only phases
- Various test changes and fixes to account for the differences in SQL
  (like how foreign keys need to exist)

This deliberately doesn't do anything to alter the objects actually
stored in the DB yet, just how we use them

docs/flows.md

@@ -31,8 +31,6 @@ An EPP flow that creates a new contact.
     *   Resource with this id already exists.
 *   2306
     *   Declining contact disclosure is disallowed by server policy.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## ContactDeleteFlow
 
@@ -59,8 +57,6 @@ or failure message when the process is complete.
     *   Resource status prohibits this operation.
 *   2305
     *   Resource to be deleted has active incoming references.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## ContactInfoFlow
 
@@ -107,8 +103,6 @@ transfer request, which then becomes effective immediately.
     *   The resource does not have a pending transfer.
 *   2303
     *   Resource with this id does not exist.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## ContactTransferCancelFlow
 
@@ -134,8 +128,6 @@ request.
     *   The resource does not have a pending transfer.
 *   2303
     *   Resource with this id does not exist.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## ContactTransferQueryFlow
 
@@ -186,8 +178,6 @@ that window, this flow allows the losing client to reject the transfer request.
     *   The resource does not have a pending transfer.
 *   2303
     *   Resource with this id does not exist.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## ContactTransferRequestFlow
 
@@ -216,8 +206,6 @@ or rejected, and the gaining registrar can also cancel the transfer request.
     *   Resource with this id does not exist.
 *   2304
     *   Resource status prohibits this operation.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## ContactUpdateFlow
 
@@ -244,8 +232,6 @@ An EPP flow that updates a contact.
 *   2306
     *   Cannot add and remove the same value.
     *   Declining contact disclosure is disallowed by server policy.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainCheckFlow
 
@@ -410,8 +396,6 @@ An EPP flow that creates a new domain resource.
     *   Too many nameservers set on this domain.
     *   Domain labels cannot end with a dash.
     *   Only encoded signed marks are supported.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainDeleteFlow
 
@@ -436,8 +420,6 @@ An EPP flow that deletes a domain.
     *   Resource status prohibits this operation.
 *   2305
     *   Domain to be deleted has subordinate hosts.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainInfoFlow
 
@@ -514,8 +496,6 @@ comes in at the exact millisecond that the domain would have expired.
 *   2306
     *   Periods for domain registrations must be specified in years.
     *   The requested fees cannot be provided in the requested currency.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainRestoreRequestFlow
 
@@ -577,8 +557,6 @@ regardless of what the original expiration time was.
     *   Domain is not eligible for restore.
 *   2306
     *   The requested fees cannot be provided in the requested currency.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainTransferApproveFlow
 
@@ -610,8 +588,6 @@ replaced with new ones with the correct approval time.
     *   The resource does not have a pending transfer.
 *   2303
     *   Resource with this id does not exist.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainTransferCancelFlow
 
@@ -642,8 +618,6 @@ transfer period passed. In this flow, those speculative objects are deleted.
     *   The resource does not have a pending transfer.
 *   2303
     *   Resource with this id does not exist.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainTransferQueryFlow
 
@@ -699,8 +673,6 @@ transfer period passed. In this flow, those speculative objects are deleted.
     *   The resource does not have a pending transfer.
 *   2303
     *   Resource with this id does not exist.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainTransferRequestFlow
 
@@ -762,8 +734,6 @@ new ones with the correct approval time).
         EPP extension.
     *   Periods for domain registrations must be specified in years.
     *   The requested fees cannot be provided in the requested currency.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## DomainUpdateFlow
 
@@ -822,8 +792,6 @@ statuses are updated at once.
     *   The secDNS:all element must have value 'true' if present.
     *   Too many DS records set on a domain.
     *   Too many nameservers set on this domain.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## HelloFlow
 
@@ -886,8 +854,6 @@ allows creating a host name, and if necessary enqueues tasks to update DNS.
     *   Superordinate domain for this hostname is in pending delete.
 *   2306
     *   Host names must be at least two levels below the registry suffix.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## HostDeleteFlow
 
@@ -918,8 +884,6 @@ or failure message when the process is complete.
     *   Resource status prohibits this operation.
 *   2305
     *   Resource to be deleted has active incoming references.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## HostInfoFlow
 
@@ -992,8 +956,6 @@ are enqueued to update DNS accordingly.
 *   2306
     *   Cannot add and remove the same value.
     *   Host names must be at least two levels below the registry suffix.
-*   2400
-    *   Registry is currently undergoing maintenance and is in read-only mode.
 
 ## LoginFlow