[DO NOT COMMIT] Revert "Add comma missing from #15382. (#15429)"

This reverts commit 38272be.

This demonstartes that this PR would have spotted the underlying error.

Author: David Robertson

changelog.d/15429.misc

@@ -1712,7 +1712,7 @@ def _delete_old_forward_extrem_cache_txn(txn: LoggingTransaction) -> None:
                 DELETE FROM stream_ordering_to_exterm
                 WHERE stream_ordering < ?
             """
-            txn.execute(sql, (self.stream_ordering_month_ago,))
+            txn.execute(sql, self.stream_ordering_month_ago)
 
         await self.db_pool.runInteraction(
             "_delete_old_forward_extrem_cache",