No need for the extra join since membership is built-in to `current_s…

…tate_events`

`current_state_events` was added in #5706
and #13745

synapse/storage/databases/main/roommember.py

@@ -927,11 +927,10 @@ async def _check_host_room_membership(
             raise Exception("Invalid host name")
 
         sql = """
-            SELECT state_key FROM current_state_events AS c
-            INNER JOIN room_memberships AS m USING (event_id)
-            WHERE m.membership = ?
+            SELECT state_key FROM current_state_events
+            WHERE membership = ?
                 AND type = 'm.room.member'
-                AND c.room_id = ?
+                AND room_id = ?
                 AND state_key LIKE ?
             LIMIT 1
         """