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

modules/audio_device/linux/audio_device_alsa_linux.h

Index: modules/audio_device/linux/audio_device_alsa_linux.h
diff --git a/modules/audio_device/linux/audio_device_alsa_linux.h b/modules/audio_device/linux/audio_device_alsa_linux.h
index 96a15ebac13860218221a847e4d6282339097e39..05871f036565b16b9b1315b53d8d0701c39c50b0 100644
--- a/modules/audio_device/linux/audio_device_alsa_linux.h
+++ b/modules/audio_device/linux/audio_device_alsa_linux.h
@@ -125,15 +125,6 @@ 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:
@@ -206,11 +197,6 @@ private:
     snd_pcm_sframes_t _recordingDelay;
     snd_pcm_sframes_t _playoutDelay;
 
-    uint16_t _playWarning;
-    uint16_t _playError;
-    uint16_t _recWarning;
-    uint16_t _recError;
-
     char _oldKeyState[32];
 #if defined(USE_X11)
     Display* _XDisplay;