Use stream rather depth ordering for push actions

This simplifies things as it is, but will also allow us to change the
way we traverse topologically without having to update the way push
actions work.

synapse/storage/receipts.py

@@ -407,7 +407,6 @@ class ReceiptsStore(ReceiptsWorkerStore):
                 txn,
                 room_id=room_id,
                 user_id=user_id,
-                topological_ordering=topological_ordering,
                 stream_ordering=stream_ordering,
             )