Remove the VoiceEngineObserver callback interface.

audio/audio_state.h

Index: audio/audio_state.h
diff --git a/audio/audio_state.h b/audio/audio_state.h
index 16d66380e2e3bf085baf944a27dbf214dcb0b939..c9c2cc561e9e63b445a34d2ffcc8ad44ea010283 100644
--- a/audio/audio_state.h
+++ b/audio/audio_state.h
@@ -22,8 +22,7 @@
 namespace webrtc {
 namespace internal {
 
-class AudioState final : public webrtc::AudioState,
-                         public webrtc::VoiceEngineObserver {
+class AudioState final : public webrtc::AudioState {
  public:
   explicit AudioState(const AudioState::Config& config);
   ~AudioState() override;
@@ -42,9 +41,6 @@ class AudioState final : public webrtc::AudioState,
   int AddRef() const override;
   int Release() const override;
 
-  // webrtc::VoiceEngineObserver implementation.
-  void CallbackOnError(int channel_id, int err_code) override;
-
   rtc::ThreadChecker thread_checker_;
   rtc::ThreadChecker process_thread_checker_;
   const webrtc::AudioState::Config config_;
@@ -52,11 +48,6 @@ class AudioState final : public webrtc::AudioState,
   // We hold one interface pointer to the VoE to make sure it is kept alive.
   ScopedVoEInterface<VoEBase> voe_base_;
 
-  // The critical section isn't strictly needed in this case, but xSAN bots may
-  // trigger on unprotected cross-thread access.
-  rtc::CriticalSection crit_sect_;
-  bool typing_noise_detected_ RTC_GUARDED_BY(crit_sect_) = false;
-
   // Reference count; implementation copied from rtc::RefCountedObject.
   mutable volatile int ref_count_ = 0;