Remove unused variables from remoting protocol unittest

https://chromium-review.googlesource.com/c/chromium/src/+/721889/3 was not enough to get the clang tot bots green.

TBR=thakis@chromium.org,hans@chromium.org,sergeyu@chromium.org
NOPRESUBMIT=true
NOTRY=true

Change-Id: I7dec2af6cea5664cc218fb97c59bb2406312f10a
Reviewed-on: https://chromium-review.googlesource.com/722282
Commit-Queue: Reid Kleckner <rnk@chromium.org>
Reviewed-by: Reid Kleckner <rnk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509195}

remoting/protocol/session_config.cc

@@ -83,10 +83,6 @@ std::unique_ptr<SessionConfig> SessionConfig::SelectCommon(
     return nullptr;
 
   std::unique_ptr<SessionConfig> result(new SessionConfig(Protocol::ICE));
-  ChannelConfig control_config;
-  ChannelConfig event_config;
-  ChannelConfig video_config;
-  ChannelConfig audio_config;
 
   // If neither host nor the client have VP9 experiment enabled then remove it
   // from the list of host video configs.