AbstractChangeUpdate: Set author/committer in superclass

This is always set to the same value. Don't rely on implementations to
set it, just do it once in the wrapper.

Change-Id: I963f5130215b2b8114e8d8729824371e6e182041

gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeDraftUpdate.java

@@ -234,8 +234,6 @@ public class ChangeDraftUpdate extends AbstractChangeUpdate {
   protected CommitBuilder applyImpl(ObjectInserter ins)
       throws OrmException, IOException {
     CommitBuilder cb = new CommitBuilder();
-    cb.setAuthor(newAuthorIdent());
-    cb.setCommitter(new PersonIdent(serverIdent, when));
     cb.setMessage("Update draft comments");
     AtomicBoolean removedAllComments = new AtomicBoolean();
     ObjectId treeId = storeCommentsInNotes(ins, removedAllComments);