Remove PatchSetAncestors table

The only remaining callers are the insert and delete code paths; it is
no longer used for lookups.

Change-Id: Id665eda39b585750f1b4032312ea04f5539456b4

gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeInserter.java

@@ -245,7 +245,6 @@ public class ChangeInserter extends BatchUpdate.InsertChangeOp {
     ReviewDb db = ctx.getDb();
     ChangeControl ctl = ctx.getChangeControl();
     ChangeUpdate update = ctx.getChangeUpdate();
-    ChangeUtil.insertAncestors(db, patchSet.getId(), commit);
     if (patchSet.getGroups() == null) {
       patchSet.setGroups(GroupCollector.getDefaultGroups(patchSet));
     }