Removing forward declarations that are never referenced.

Bug: None
Change-Id: I0f472f55671e92d824c672f3c3b1bc083b8440fc
Reviewed-on: https://webrtc-review.googlesource.com/22004
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20631}
diff --git a/api/audio_codecs/audio_encoder.h b/api/audio_codecs/audio_encoder.h
index 4e4c409..7ad9ba4 100644
--- a/api/audio_codecs/audio_encoder.h
+++ b/api/audio_codecs/audio_encoder.h
@@ -24,7 +24,6 @@
 
 namespace webrtc {
 
-class Clock;
 class RtcEventLog;
 
 // Statistics related to Audio Network Adaptation.
diff --git a/media/engine/webrtcvideoengine.h b/media/engine/webrtcvideoengine.h
index f9c053a..751dc4f 100644
--- a/media/engine/webrtcvideoengine.h
+++ b/media/engine/webrtcvideoengine.h
@@ -65,8 +65,6 @@
 class WebRtcVoiceEngine;
 class WebRtcVoiceMediaChannel;
 
-struct Device;
-
 class UnsignalledSsrcHandler {
  public:
   enum Action {