Remove extra related changes

See matrix-org/synapse#11243
Also see matrix-org/synapse#9247

Author: MadLittleMods

synapse/handlers/message.py

@@ -1222,7 +1222,6 @@ async def create_new_client_event(
         if state_event_ids is not None:
             # Do a quick check to make sure that prev_event_ids is present to
             # make the type-checking around `builder.build` happy.
-            # prev_event_ids could be an empty array though.
             assert prev_event_ids is not None
 
             temp_event = await builder.build(

synapse/handlers/room_member.py

@@ -916,7 +916,6 @@ async def update_membership_locked(
                     )
                 # InviteRule.IGNORE is handled at the sync layer.
 
-        # An empty prev_events list is allowed as long as the auth_event_ids are present
         if prev_event_ids is not None:
             return await self._local_membership_update(
                 requester=requester,