Remove AudioDeviceObserver and make ADM not inherit from the Module interface.

modules/audio_device/dummy/audio_device_dummy.cc

Index: modules/audio_device/dummy/audio_device_dummy.cc
diff --git a/modules/audio_device/dummy/audio_device_dummy.cc b/modules/audio_device/dummy/audio_device_dummy.cc
index cb41e4a9b843b62bd80f98dcb3d68ec75a5a2f80..7ababa166706e3eeaf37a239ad5b0a5dd9ccb039 100644
--- a/modules/audio_device/dummy/audio_device_dummy.cc
+++ b/modules/audio_device/dummy/audio_device_dummy.cc
@@ -158,21 +158,5 @@ int32_t AudioDeviceDummy::PlayoutDelay(uint16_t& delayMS) const { return -1; }
 
 int32_t AudioDeviceDummy::RecordingDelay(uint16_t& delayMS) const { return -1; }
 
-bool AudioDeviceDummy::PlayoutWarning() const { return false; }
-
-bool AudioDeviceDummy::PlayoutError() const { return false; }
-
-bool AudioDeviceDummy::RecordingWarning() const { return false; }
-
-bool AudioDeviceDummy::RecordingError() const { return false; }
-
-void AudioDeviceDummy::ClearPlayoutWarning() {}
-
-void AudioDeviceDummy::ClearPlayoutError() {}
-
-void AudioDeviceDummy::ClearRecordingWarning() {}
-
-void AudioDeviceDummy::ClearRecordingError() {}
-
 void AudioDeviceDummy::AttachAudioBuffer(AudioDeviceBuffer* audioBuffer) {}
 }  // namespace webrtc