ChangeNotesState: Remove redundant revertOf field

This is a @Column in Change and thus belongs in ChangeColumns. In
ChangeNotes#create it reuses the same value in both places, so they
should always be equal, modulo missing ChangeColumns, in which case the
field in ChangeNotesState should never be accessed.

Change-Id: I63eb5acdcd6c47ea2ceea7d830d5b5b6e4b28d2f

java/com/google/gerrit/server/notedb/ChangeNotes.java

@@ -679,7 +679,7 @@ public class ChangeNotes extends AbstractChangeNotes<ChangeNotes> {
   }
 
   public Change.Id getRevertOf() {
-    return state.revertOf();
+    return state.columns().revertOf();
   }
 
   public boolean hasReviewStarted() {

java/com/google/gerrit/server/notedb/ChangeNotesState.java

@@ -75,7 +75,6 @@ public abstract class ChangeNotesState {
         ImmutableList.of(),
         ImmutableListMultimap.of(),
         ImmutableListMultimap.of(),
-        null,
         null);
   }
 
@@ -147,8 +146,7 @@ public abstract class ChangeNotesState {
         ImmutableList.copyOf(allChangeMessages),
         ImmutableListMultimap.copyOf(changeMessagesByPatchSet),
         ImmutableListMultimap.copyOf(publishedComments),
-        readOnlyUntil,
-        revertOf);
+        readOnlyUntil);
   }
 
   /**
@@ -244,9 +242,6 @@ public abstract class ChangeNotesState {
   @Nullable
   abstract Timestamp readOnlyUntil();
 
-  @Nullable
-  abstract Change.Id revertOf();
-
   Change newChange(Project.NameKey project) {
     ChangeColumns c = checkNotNull(columns(), "columns are required");
     Change change =