Remove no-op send_command for Redis replication. (#15274)

With Redis commands do not need to be re-issued by the main
process (they fan-out to all processes at once) and thus it is no
longer necessary to worry about them reflecting recursively forever.

tests/replication/tcp/test_remote_server_up.py

@@ -1,63 +0,0 @@
-# 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.
-
-from typing import Tuple
-
-from twisted.internet.address import IPv4Address
-from twisted.internet.interfaces import IProtocol
-from twisted.test.proto_helpers import MemoryReactor, StringTransport
-
-from synapse.replication.tcp.resource import ReplicationStreamProtocolFactory
-from synapse.server import HomeServer
-from synapse.util import Clock
-
-from tests.unittest import HomeserverTestCase
-
-
-class RemoteServerUpTestCase(HomeserverTestCase):
-    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
-        self.factory = ReplicationStreamProtocolFactory(hs)
-
-    def _make_client(self) -> Tuple[IProtocol, StringTransport]:
-        """Create a new direct TCP replication connection"""
-
-        proto = self.factory.buildProtocol(IPv4Address("TCP", "127.0.0.1", 0))
-        transport = StringTransport()
-        proto.makeConnection(transport)
-
-        # We can safely ignore the commands received during connection.
-        self.pump()
-        transport.clear()
-
-        return proto, transport
-
-    def test_relay(self) -> None:
-        """Test that Synapse will relay REMOTE_SERVER_UP commands to all
-        other connections, but not the one that sent it.
-        """
-
-        proto1, transport1 = self._make_client()
-
-        # We shouldn't receive an echo.
-        proto1.dataReceived(b"REMOTE_SERVER_UP example.com\n")
-        self.pump()
-        self.assertEqual(transport1.value(), b"")
-
-        # But we should see an echo if we connect another client
-        proto2, transport2 = self._make_client()
-        proto1.dataReceived(b"REMOTE_SERVER_UP example.com\n")
-
-        self.pump()
-        self.assertEqual(transport1.value(), b"")
-        self.assertEqual(transport2.value(), b"REMOTE_SERVER_UP example.com\n")