Do not attempt to bundled aggregations for /members and /state. (#11623)

Both of those APIs return state events, which will not have bundled
aggregations added anyway.

changelog.d/11623.bugfix

+Fix a long-standing bug where responses included bundled aggregations when they should not, per [MSC2675](https://github.com/matrix-org/matrix-doc/pull/2675).

synapse/handlers/message.py

@@ -246,9 +246,7 @@ class MessageHandler:
                 room_state = room_state_events[membership_event_id]
 
         now = self.clock.time_msec()
-        events = await self._event_serializer.serialize_events(
-            room_state.values(), now, bundle_aggregations=True
-        )
+        events = await self._event_serializer.serialize_events(room_state.values(), now)
         return events
 
     async def get_joined_members(self, requester: Requester, room_id: str) -> dict: