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

modules/audio_device/ios/audio_device_not_implemented_ios.mm

Index: modules/audio_device/ios/audio_device_not_implemented_ios.mm
diff --git a/modules/audio_device/ios/audio_device_not_implemented_ios.mm b/modules/audio_device/ios/audio_device_not_implemented_ios.mm
index dee3cc7119731a91e6d4cbebb911b9a025f0f60f..6dfc02bfe465caf4adca9b2907c9b88e653f24b6 100644
--- a/modules/audio_device/ios/audio_device_not_implemented_ios.mm
+++ b/modules/audio_device/ios/audio_device_not_implemented_ios.mm
@@ -91,22 +91,6 @@ int32_t AudioDeviceIOS::SetPlayoutDevice(AudioDeviceModule::WindowsDeviceType) {
   return -1;
 }
 
-bool AudioDeviceIOS::PlayoutWarning() const {
-  return false;
-}
-
-bool AudioDeviceIOS::PlayoutError() const {
-  return false;
-}
-
-bool AudioDeviceIOS::RecordingWarning() const {
-  return false;
-}
-
-bool AudioDeviceIOS::RecordingError() const {
-  return false;
-}
-
 int32_t AudioDeviceIOS::InitMicrophone() {
   return 0;
 }