Move remaining traces of VoiceEngine

- Move files from voice_engine/ to audio/.
- Rename voice_engine/utility.* to remix_resample.* since there are no other
  utilities in those files.
- Move test/mock_voe_channel_proxy.h to audio/.
- Removed voe_channel_id from Audio[Receive|Send]Stream::Config.
- Remove VoiceEngine* from AudioState::Config.
- Fix a few cpplint complaints which showed when moving files.

NOPRESUBMIT=true

Bug: webrtc:4690
Change-Id: Id266c822d956625c358fa5e193e6f4837164aef8
Reviewed-on: https://webrtc-review.googlesource.com/39268
Commit-Queue: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21657}

call/audio_state.h

@@ -19,16 +19,12 @@ namespace webrtc {
 class AudioDeviceModule;
 class AudioProcessing;
 class AudioTransport;
-class VoiceEngine;
 
 // AudioState holds the state which must be shared between multiple instances of
 // webrtc::Call for audio processing purposes.
 class AudioState : public rtc::RefCountInterface {
  public:
   struct Config {
-    // TODO(solenberg): Remove once clients don't use it anymore.
-    VoiceEngine* voice_engine = nullptr;
-
     // The audio mixer connected to active receive streams. One per
     // AudioState.
     rtc::scoped_refptr<AudioMixer> audio_mixer;