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

modules/audio_device/ios/audio_device_not_implemented_ios.mm

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 73 matching lines @@
 int32_t AudioDeviceIOS::SetPlayoutDevice(uint16_t index) {
   LOG_F(LS_WARNING) << "Not implemented";
   return 0;
 }
 
 int32_t AudioDeviceIOS::SetPlayoutDevice(AudioDeviceModule::WindowsDeviceType) {
   RTC_NOTREACHED() << "Not implemented";
   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;
 }
 
 bool AudioDeviceIOS::MicrophoneIsInitialized() const {
   return true;
 }
 
 int32_t AudioDeviceIOS::MicrophoneMuteIsAvailable(bool& available) {
   available = false;
@@ skipping 105 matching lines @@
   available = true;
   return 0;
 }
 
 int32_t AudioDeviceIOS::RecordingIsAvailable(bool& available) {
   available = true;
   return 0;
 }
 
 }  // namespace webrtc