Stop passing state event IDs around

This yields a further improvement as we don't need to lookup those
events, instead they get pulled from state.

See discussion on: #13210

synapse/handlers/room.py

@@ -884,7 +884,6 @@ async def create_room(
         (
             last_stream_id,
             last_sent_event_id,
-            state_event_ids,
             depth,
         ) = await self._send_events_for_new_room(
             requester,
@@ -915,11 +914,9 @@ async def create_room(
                 },
                 ratelimit=False,
                 prev_event_ids=[last_sent_event_id],
-                state_event_ids=state_event_ids.copy(),
                 depth=depth,
             )
             last_sent_event_id = name_event.event_id
-            state_event_ids.append(name_event.event_id)
             depth += 1
 
         if "topic" in config:
@@ -938,11 +935,9 @@ async def create_room(
                 },
                 ratelimit=False,
                 prev_event_ids=[last_sent_event_id],
-                state_event_ids=state_event_ids.copy(),
                 depth=depth,
             )
             last_sent_event_id = topic_event.event_id
-            state_event_ids.append(topic_event.event_id)
             depth += 1
 
         # we avoid dropping the lock between invites, as otherwise joins can
@@ -969,10 +964,8 @@ async def create_room(
                     content=content,
                     new_room=True,
                     prev_event_ids=[last_sent_event_id],
-                    state_event_ids=state_event_ids.copy(),
                     depth=depth,
                 )
-                state_event_ids.append(last_sent_event_id)
                 depth += 1
 
         for invite_3pid in invite_3pid_list:
@@ -1034,7 +1027,6 @@ async def _send_events_for_new_room(
         event_keys = {"room_id": room_id, "sender": creator_id, "state_key": ""}
 
         depth = 1
-        state_event_ids: List[str] = []
         last_sent_event_id: Optional[str] = None
 
         def create(etype: str, content: JsonDict, **kwargs: Any) -> JsonDict:
@@ -1186,7 +1178,7 @@ async def send(etype: str, content: JsonDict, **kwargs: Any) -> int:
                 content={"algorithm": RoomEncryptionAlgorithms.DEFAULT},
             )
 
-        return last_sent_stream_id, last_sent_event_id, state_event_ids, depth
+        return last_sent_stream_id, last_sent_event_id, depth
 
     def _generate_room_id(self) -> str:
         """Generates a random room ID.