Remove method getNumberOfPatchSets() from Change.

Removed the only use of the method. Fixed RebaseChange to pass in
the db object.

Some other minor cleanups are included too.

This is part of the code cleanup to remove the nbrPatchSets field.

Change-Id: Iaa7431ea9c96e19c008d8ec25d774e0f7240ba35

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java

@@ -436,10 +436,6 @@ public final class Change {
     lastUpdatedOn = new Timestamp(System.currentTimeMillis());
   }
 
-  public int getNumberOfPatchSets() {
-    return nbrPatchSets;
-  }
-
   public String getSortKey() {
     return sortKey;
   }