Fix variable issue.

Author: clokep

synapse/storage/databases/main/event_push_actions.py

@@ -318,9 +318,7 @@ async def _background_drop_null_thread_id_indexes(
         event_push_summary.
         """
 
-        def drop_null_thread_id_indexes_txn(
-            txn: LoggingTransaction, start_stream_ordering: int
-        ) -> None:
+        def drop_null_thread_id_indexes_txn(txn: LoggingTransaction) -> None:
             sql = "DROP INDEX IF EXISTS event_push_actions_thread_id_null"
             logger.debug("[SQL] %s", sql)
             txn.execute(sql)