Remove unused tables `room_stats_historical` and `user_stats_historical` (#11280)

* remove unused tables room_stats_historical and user_stats_historical

* update changelog number

* Bump schema compat version comment

* make linter happy

* Update comment to give more info

Co-authored-by: reivilibre <oliverw@matrix.org>

Co-authored-by: reivilibre <oliverw@matrix.org>

changelog.d/11280.misc

@@ -0,0 +1 @@
+Drop unused db tables `room_stats_historical` and `user_stats_historical`.

synapse/storage/schema/__init__.py

@@ -45,10 +45,13 @@ Changes in SCHEMA_VERSION = 64:
 Changes in SCHEMA_VERSION = 65:
     - MSC2716: Remove unique event_id constraint from insertion_event_edges
       because an insertion event can have multiple edges.
+    - Remove unused tables `user_stats_historical` and `room_stats_historical`.
 """
 
 
-SCHEMA_COMPAT_VERSION = 60  # 60: "outlier" not in internal_metadata.
+SCHEMA_COMPAT_VERSION = (
+    61  # 61: Remove unused tables `user_stats_historical` and `room_stats_historical`
+)
 """Limit on how far the synapse codebase can be rolled back without breaking db compat
 
 This value is stored in the database, and checked on startup. If the value in the

synapse/storage/schema/main/delta/65/05_remove_room_stats_historical_and_user_stats_historical.sql

@@ -0,0 +1,19 @@
+/* Copyright 2021 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.
+ */
+
+ -- Remove unused tables room_stats_historical and user_stats_historical
+ -- which have not been read or written since schema version 61.
+ DROP TABLE IF EXISTS room_stats_historical;
+ DROP TABLE IF EXISTS user_stats_historical;