Disable reduced-size RTCP in default config.

Verifies that reduced-size isn't configured in WebRtcVideoEngine2
without explicit configuration (which doesn't exist). Also disables REMB
in the default config because it requires reconfiguration.

Adds default-config tests to make sure that they don't contain
parameters that need to be negotiated between clients.

BUG=chromium:497103, webrtc:4745
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1171533002

Cr-Commit-Position: refs/heads/master@{#9384}

webrtc/test/call_test.cc

@@ -108,6 +108,7 @@ void CallTest::CreateMatchingReceiveConfigs() {
   assert(receive_configs_.empty());
   assert(allocated_decoders_.empty());
   VideoReceiveStream::Config config;
+  config.rtp.remb = true;
   config.rtp.local_ssrc = kReceiverLocalSsrc;
   for (const RtpExtension& extension : send_config_.rtp.extensions)
     config.rtp.extensions.push_back(extension);