Remove MockRemoteBitrateObserver (unused)

webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.h

Index: webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.h
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.h b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.h
index 31d796225a2b5cbb79c27044e009e2ddd8c82ee2..b893f56ed13d2c44c17299b1269a898fc3902473 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.h
+++ b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.h
@@ -56,12 +56,12 @@ class RemoteBitrateEstimatorSingleStream : public RemoteBitrateEstimator {
   // otherwise creates it.
   AimdRateControl* GetRemoteRate() EXCLUSIVE_LOCKS_REQUIRED(crit_sect_.get());
 
-  Clock* clock_;
+  Clock* const clock_;
   SsrcOveruseEstimatorMap overuse_detectors_ GUARDED_BY(crit_sect_.get());
   RateStatistics incoming_bitrate_ GUARDED_BY(crit_sect_.get());
   uint32_t last_valid_incoming_bitrate_ GUARDED_BY(crit_sect_.get());
   std::unique_ptr<AimdRateControl> remote_rate_ GUARDED_BY(crit_sect_.get());
-  RemoteBitrateObserver* observer_ GUARDED_BY(crit_sect_.get());
+  RemoteBitrateObserver* const observer_ GUARDED_BY(crit_sect_.get());
   std::unique_ptr<CriticalSectionWrapper> crit_sect_;
   int64_t last_process_time_;
   int64_t process_interval_ms_ GUARDED_BY(crit_sect_.get());