Remove presence lists (#4989)

Remove presence list support as per MSC 1819

synapse/storage/schema/delta/54/drop_presence_list.sql

@@ -0,0 +1,16 @@
+/* Copyright 2019 New Vector 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.
+ */
+
+DROP TABLE IF EXISTS presence_list;

synapse/storage/schema/full_schemas/16/presence.sql

@@ -28,13 +28,5 @@ CREATE TABLE IF NOT EXISTS presence_allow_inbound(
   UNIQUE (observed_user_id, observer_user_id)
 );
 
--- For each of /my/ users (watcher), which possibly-remote users are they
--- watching?
-CREATE TABLE IF NOT EXISTS presence_list(
-  user_id TEXT NOT NULL,
-  observed_user_id TEXT NOT NULL, -- a UserID,
-  accepted BOOLEAN NOT NULL,
-  UNIQUE (user_id, observed_user_id)
-);
-
-CREATE INDEX presence_list_user_id ON presence_list (user_id);
+-- We used to create a table called presence_list, but this is no longer used 
+-- and is removed in delta 54.