Remove incorrect migration file from `state` logical DB (#13788)

* Remove incorrect migration file from `state` logical DB

The table `ex_outlier_stream` is part of the `main` logical DB; it
should not have been created in the `state` logical DB. We remove this
migration now as a tidy-up.

Note: we cannot `DROP TABLE IF EXISTS ex_outlier_stream` in a new
migration, because some (most) instances of Synapse host both of these
logical DBs on the same DB cluster.

* Changelog

changelog.d/13788.misc

+Remove an old, incorrect migration file.

synapse/storage/schema/state/delta/30/state_stream.sql

-/* Copyright 2016 OpenMarket Ltd
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-
-/* We used to create a table called current_state_resets, but this is no
- * longer used and is removed in delta 54.
- */
-
-/* The outlier events that have aquired a state group typically through
- * backfill. This is tracked separately to the events table, as assigning a
- * state group change the position of the existing event in the stream
- * ordering.
- * However since a stream_ordering is assigned in persist_event for the
- * (event, state) pair, we can use that stream_ordering to identify when
- * the new state was assigned for the event.
- */
-
-/* NB: This table belongs to the `main` logical database; it should not be present
- * in `state`.
- */
-CREATE TABLE IF NOT EXISTS ex_outlier_stream(
-    event_stream_ordering BIGINT PRIMARY KEY NOT NULL,
-    event_id TEXT NOT NULL,
-    state_group BIGINT NOT NULL
-);