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

modules/audio_device/ios/audio_device_ios.h

Index: modules/audio_device/ios/audio_device_ios.h
diff --git a/modules/audio_device/ios/audio_device_ios.h b/modules/audio_device/ios/audio_device_ios.h
index caaeaace00be16ac8177dd6fa860009c1457bc66..8235bf0d1b4a5c1771765d6341a6865704859fe3 100644
--- a/modules/audio_device/ios/audio_device_ios.h
+++ b/modules/audio_device/ios/audio_device_ios.h
@@ -139,14 +139,6 @@ class AudioDeviceIOS : public AudioDeviceGeneric,
   int32_t StereoRecordingIsAvailable(bool& available) override;
   int32_t SetStereoRecording(bool enable) override;
   int32_t StereoRecording(bool& enabled) 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 {}
 
   // AudioSessionObserver methods. May be called from any thread.
   void OnInterruptionBegin() override;