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

modules/audio_device/include/audio_device_defines.h

Index: modules/audio_device/include/audio_device_defines.h
diff --git a/modules/audio_device/include/audio_device_defines.h b/modules/audio_device/include/audio_device_defines.h
index 133819ac334824474c11d29b8c4bef0376937364..510b07c049f152fa4eafe403c6a05fd57eb22222 100644
--- a/modules/audio_device/include/audio_device_defines.h
+++ b/modules/audio_device/include/audio_device_defines.h
@@ -24,22 +24,6 @@ static const int kAdmMaxGuidSize = 128;
 static const int kAdmMinPlayoutBufferSizeMs = 10;
 static const int kAdmMaxPlayoutBufferSizeMs = 250;
 
-// ----------------------------------------------------------------------------
-//  AudioDeviceObserver
-// ----------------------------------------------------------------------------
-
-class AudioDeviceObserver {
- public:
-  enum ErrorCode { kRecordingError = 0, kPlayoutError = 1 };
-  enum WarningCode { kRecordingWarning = 0, kPlayoutWarning = 1 };
-
-  virtual void OnErrorIsReported(const ErrorCode error) = 0;
-  virtual void OnWarningIsReported(const WarningCode warning) = 0;
-
- protected:
-  virtual ~AudioDeviceObserver() {}
-};
-
 // ----------------------------------------------------------------------------
 //  AudioTransport
 // ----------------------------------------------------------------------------