Remove unused store method get_hosts_in_room (#7448)

Author: anoadragon453

changelog.d/7448.misc

@@ -0,0 +1 @@
+Remove storage method `get_hosts_in_room` that is no longer called anywhere.

synapse/storage/data_stores/main/roommember.py

@@ -153,16 +153,6 @@ def _check_safe_current_state_events_membership_updated_txn(self, txn):
                 self._check_safe_current_state_events_membership_updated_txn,
             )
 
-    @cachedInlineCallbacks(max_entries=100000, iterable=True, cache_context=True)
-    def get_hosts_in_room(self, room_id, cache_context):
-        """Returns the set of all hosts currently in the room
-        """
-        user_ids = yield self.get_users_in_room(
-            room_id, on_invalidate=cache_context.invalidate
-        )
-        hosts = frozenset(get_domain_from_id(user_id) for user_id in user_ids)
-        return hosts
-
     @cached(max_entries=100000, iterable=True)
     def get_users_in_room(self, room_id):
         return self.db.runInteraction(