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

…_state_events` (#15731)

This helps with the upstream `is_host_joined()` and `is_host_invited()` functions.

`membership` was added to `current_state_events` in #5706 and forced in #13745

changelog.d/15731.misc

@@ -0,0 +1 @@
+Remove redundant table join with `room_memberships` when doing a `is_host_joined()`/`is_host_invited()` call (`membership` is already part of the `current_state_events`).

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
         """