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

modules/audio_device/dummy/file_audio_device.cc

Index: modules/audio_device/dummy/file_audio_device.cc
diff --git a/modules/audio_device/dummy/file_audio_device.cc b/modules/audio_device/dummy/file_audio_device.cc
index 21947485648d34ec37dc7df79a8778b887954c4e..7b3e17ec7517ffcbeea647ded4a11e45e627ca5f 100644
--- a/modules/audio_device/dummy/file_audio_device.cc
+++ b/modules/audio_device/dummy/file_audio_device.cc
@@ -398,22 +398,6 @@ int32_t FileAudioDevice::PlayoutDelay(uint16_t& delayMS) const {
 
 int32_t FileAudioDevice::RecordingDelay(uint16_t& delayMS) const { return -1; }
 
-bool FileAudioDevice::PlayoutWarning() const { return false; }
-
-bool FileAudioDevice::PlayoutError() const { return false; }
-
-bool FileAudioDevice::RecordingWarning() const { return false; }
-
-bool FileAudioDevice::RecordingError() const { return false; }
-
-void FileAudioDevice::ClearPlayoutWarning() {}
-
-void FileAudioDevice::ClearPlayoutError() {}
-
-void FileAudioDevice::ClearRecordingWarning() {}
-
-void FileAudioDevice::ClearRecordingError() {}
-
 void FileAudioDevice::AttachAudioBuffer(AudioDeviceBuffer* audioBuffer) {
   rtc::CritScope lock(&_critSect);