Drop incorrectly-added table `local_rejections_stream`. (#7816)

changelog.d/7816.bugfix

+Drop table `local_rejections_stream` which was incorrectly added in Synapse 1.16.0.

synapse/storage/data_stores/main/schema/delta/58/10drop_local_rejections_stream.sql

+/* Copyright 2020 The Matrix.org Foundation C.I.C
+ *
+ * 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.
+ */
+
+/*
+The version of synapse 1.16.0 on pypi incorrectly contained a migration which
+added a table called 'local_rejections_stream'. This table is not used, and
+we drop it here for anyone who was affected.
+*/
+
+DROP TABLE IF NOT EXISTS local_rejections_stream;