Remove datastore related code (#1906)

docs/code-structure.md

@@ -77,14 +77,14 @@ The following cursor types are defined:
 *   **`SYNC_REGISTRAR_SHEET`** - Tracks the last time the registrar spreadsheet
     was successfully synced.
 
-All `Cursor` entities in Datastore contain a `DateTime` that represents the next
-timestamp at which an operation should resume processing and a `CursorType` that
-identifies which operation the cursor is associated with. In many cases, there
-are multiple cursors per operation; for instance, the cursors related to RDE
-reporting, staging, and upload are per-TLD cursors. To accomplish this, each
+All `Cursor` entities in the database contain a `DateTime` that represents the
+next timestamp at which an operation should resume processing and a `CursorType`
+that identifies which operation the cursor is associated with. In many cases,
+there are multiple cursors per operation; for instance, the cursors related to
+RDE reporting, staging, and upload are per-TLD cursors. To accomplish this, each
 `Cursor` also has a scope, a `Key<ImmutableObject>` to which the particular
 cursor applies (this can be e.g. a `Registry` or any other `ImmutableObject` in
-Datastore, depending on the operation). If the `Cursor` applies to the entire
+the database, depending on the operation). If the `Cursor` applies to the entire
 registry environment, it is considered a global cursor and has a scope of
 `EntityGroupRoot.getCrossTldKey()`.
 
@@ -172,27 +172,14 @@ objects by their unique IDs:
 *   `Host`: fully-qualified host name
 
 Since all `EppResource` entities are indexed on ROID (which is also unique, but
-not as useful as the resource's name), a `ForeignKeyIndex` provides a way to
+not as useful as the resource's name), the `ForeignKeyUtils` provides a way to
 look up the resources using another key which is also unique during the lifetime
 of the resource (though not for all time).
 
-A `ForeignKeyIndex` is updated as a resource is created or deleted. It is
-important to note that throughout the lifecycle of an `EppResource`, the
-underlying Datastore entity is never hard-deleted; its deletion time is set to
-the time at which the EPP command to delete the resource was set, and it remains
-in Datastore. Other resources with that same name can then be created.
-
-## EPP resource index
-
-An `EppResourceIndex` is an index that allows for quick enumeration of all
-`EppResource` entities in Datastore. Datastore does not otherwise provide an
-easy way to efficiently and strongly consistently enumerate all entities of a
-given type. Each `EppResourceIndex` is assigned randomly to an
-`EppResourceIndexBucket` upon creation, the number of which is configured to be
-greater than the number of shards typically used for Mapreduces that enumerate
-these entities. Mapreduces that process all `EppResource` entities (or
-subclasses thereof) distribute each `EppResourceIndexBucket` to available
-shards.
+It is important to note that throughout the lifecycle of an `EppResource`, the
+underlying entity is never hard-deleted; its deletion time is set to the time at
+which the EPP command to delete the resource was set, and it remains in the
+database. Other resources with that same name can then be created.
 
 ## History entries
 
@@ -232,7 +219,7 @@ between the registry and registrars. Refer to [RFC 5730 Section
 2.9.2.3](https://tools.ietf.org/html/rfc5730#section-2.9.2.3) for their protocol
 specification.
 
-Poll messages are stored by the system as entities in Datastore. All poll
+Poll messages are stored by the system as entities in the database. All poll
 messages have an event time at which they become active; any poll request before
 that time will not return the poll message. For example, every domain when
 created enqueues a speculative poll message for the automatic renewal of the