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

modules/audio_device/dummy/audio_device_dummy.h

Index: modules/audio_device/dummy/audio_device_dummy.h
diff --git a/modules/audio_device/dummy/audio_device_dummy.h b/modules/audio_device/dummy/audio_device_dummy.h
index 586572018386292c0d58398c46ec01f385d23673..5e2cecfa8f6c5eecc94a8080172a3478cd1294f0 100644
--- a/modules/audio_device/dummy/audio_device_dummy.h
+++ b/modules/audio_device/dummy/audio_device_dummy.h
@@ -111,15 +111,6 @@ class AudioDeviceDummy : public AudioDeviceGeneric {
   int32_t PlayoutDelay(uint16_t& delayMS) const override;
   int32_t RecordingDelay(uint16_t& delayMS) const override;
 
-  bool PlayoutWarning() const override;
-  bool PlayoutError() const override;
-  bool RecordingWarning() const override;
-  bool RecordingError() const override;
-  void ClearPlayoutWarning() override;
-  void ClearPlayoutError() override;
-  void ClearRecordingWarning() override;
-  void ClearRecordingError() override;
-
   void AttachAudioBuffer(AudioDeviceBuffer* audioBuffer) override;
 };