Registry should not be a BackupGroupRoot

In [] I made Registry a BGR in prep for each Registry being in
its own entity group. But we decided not to do that, and in []
mcilwain@ moved Registry under the cross-tld root. So there's no reason
for Registry to implement BackupGroupRoot anymore.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120402417

java/com/google/domain/registry/model/registry/Registry.java

@@ -41,9 +41,9 @@ import com.google.common.collect.Iterables;
 import com.google.common.collect.Ordering;
 import com.google.common.net.InternetDomainName;
 import com.google.domain.registry.config.RegistryEnvironment;
-import com.google.domain.registry.model.BackupGroupRoot;
 import com.google.domain.registry.model.Buildable;
 import com.google.domain.registry.model.CreateAutoTimestamp;
+import com.google.domain.registry.model.ImmutableObject;
 import com.google.domain.registry.model.common.EntityGroupRoot;
 import com.google.domain.registry.model.common.TimedTransitionProperty;
 import com.google.domain.registry.model.common.TimedTransitionProperty.TimedTransition;
@@ -71,7 +71,7 @@ import java.util.Set;
 /** Persisted per-TLD configuration data. */
 @Cache(expirationSeconds = RECOMMENDED_MEMCACHE_EXPIRATION)
 @Entity
-public class Registry extends BackupGroupRoot implements Buildable {
+public class Registry extends ImmutableObject implements Buildable {
 
   @Parent
   Key<EntityGroupRoot> parent = getCrossTldKey();

javatests/com/google/domain/registry/model/schema.txt

@@ -663,7 +663,6 @@ class com.google.domain.registry.model.registry.Registry {
   boolean escrowEnabled;
   boolean premiumPriceAckRequired;
   com.google.domain.registry.model.CreateAutoTimestamp creationTime;
-  com.google.domain.registry.model.UpdateAutoTimestamp updateTimestamp;
   com.google.domain.registry.model.common.TimedTransitionProperty<com.google.domain.registry.model.registry.Registry$TldState, com.google.domain.registry.model.registry.Registry$TldStateTransition> tldStateTransitions;
   com.google.domain.registry.model.common.TimedTransitionProperty<org.joda.money.Money, com.google.domain.registry.model.registry.Registry$BillingCostTransition> renewBillingCostTransitions;
   com.google.domain.registry.model.registry.Registry$TldType tldType;

javatests/com/google/domain/registry/tools/CreateTldCommandTest.java

@@ -66,8 +66,6 @@ public class CreateTldCommandTest extends CommandTestCase<CreateTldCommand> {
         .isEqualTo(Registry.DEFAULT_REDEMPTION_GRACE_PERIOD);
     assertThat(registry.getPendingDeleteLength()).isEqualTo(Registry.DEFAULT_PENDING_DELETE_LENGTH);
     assertThat(registry.getCreationTime()).isIn(Range.closed(before, after));
-    assertThat(registry.getUpdateAutoTimestamp().getTimestamp())
-        .isEqualTo(registry.getCreationTime());
   }
 
   @Test

javatests/com/google/domain/registry/tools/UpdateTldCommandTest.java

@@ -30,7 +30,6 @@ import static org.joda.time.Duration.standardMinutes;
 
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSortedMap;
-import com.google.common.collect.Range;
 import com.google.domain.registry.model.registry.Registry;
 import com.google.domain.registry.model.registry.Registry.TldState;
 import com.google.domain.registry.model.registry.label.PremiumList;
@@ -63,22 +62,6 @@ public class UpdateTldCommandTest extends CommandTestCase<UpdateTldCommand> {
     createTld("xn--q9jyb4c");
   }
 
-  @Test
-  public void testSuccess_updateAutoTimestamp() throws Exception {
-    Registry registry = Registry.get("xn--q9jyb4c");
-    DateTime creationTime = registry.getCreationTime();
-    assertThat(creationTime).isNotNull();
-    assertThat(registry.getUpdateAutoTimestamp().getTimestamp()).isEqualTo(creationTime);
-
-    DateTime before = DateTime.now(UTC);
-    runCommandForced("xn--q9jyb4c");
-    DateTime after = DateTime.now(UTC);
-
-    registry = Registry.get("xn--q9jyb4c");
-    assertThat(registry.getCreationTime()).isEqualTo(creationTime);
-    assertThat(registry.getUpdateAutoTimestamp().getTimestamp()).isIn(Range.closed(before, after));
-  }
-
   @Test
   public void testSuccess_tldStateTransitions() throws Exception {
     DateTime sunriseStart = now;