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

modules/audio_device/linux/audio_device_pulse_linux.h

Index: modules/audio_device/linux/audio_device_pulse_linux.h
diff --git a/modules/audio_device/linux/audio_device_pulse_linux.h b/modules/audio_device/linux/audio_device_pulse_linux.h
index 2a83b5c0a395d68d0465fedd6729e3f7f37de5ef..6fd571773fa78c4a16e80c28e4afb1ccc072169d 100644
--- a/modules/audio_device/linux/audio_device_pulse_linux.h
+++ b/modules/audio_device/linux/audio_device_pulse_linux.h
@@ -187,15 +187,6 @@ public:
     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;
 
 private:
@@ -306,10 +297,6 @@ private:
  uint32_t _sndCardRecDelay;
 
  int32_t _writeErrors;
- uint16_t _playWarning;
- uint16_t _playError;
- uint16_t _recWarning;
- uint16_t _recError;
 
  uint16_t _deviceIndex;
  int16_t _numPlayDevices;