Remove the VoiceEngineObserver callback interface.

audio/audio_receive_stream_unittest.cc

Index: audio/audio_receive_stream_unittest.cc
diff --git a/audio/audio_receive_stream_unittest.cc b/audio/audio_receive_stream_unittest.cc
index b79ae19a6c820244ee002e9deb297835f9ae0b72..69cf4591fa253ad69bb72d085e365671b3b50a8c 100644
--- a/audio/audio_receive_stream_unittest.cc
+++ b/audio/audio_receive_stream_unittest.cc
@@ -75,10 +75,6 @@ struct ConfigHelper {
         audio_mixer_(new rtc::RefCountedObject<MockAudioMixer>()) {
     using testing::Invoke;
 
-    EXPECT_CALL(voice_engine_,
-        RegisterVoiceEngineObserver(_)).WillOnce(Return(0));
-    EXPECT_CALL(voice_engine_,
-        DeRegisterVoiceEngineObserver()).WillOnce(Return(0));
     EXPECT_CALL(voice_engine_, audio_device_module());
     EXPECT_CALL(voice_engine_, audio_transport());