Update/move RTCVideoRendererAdapter to webrtc/api/objc.

webrtc/api/objc/RTCVideoRendererAdapter.h

 /*
  *  Copyright 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.
  */
 
 #import <Foundation/Foundation.h>
 
-typedef NS_ENUM(NSInteger, RTCSourceState) {
-  RTCSourceStateInitializing,
-  RTCSourceStateLive,
-  RTCSourceStateEnded,
-  RTCSourceStateMuted,
-};
-
 NS_ASSUME_NONNULL_BEGIN
 
-@interface RTCVideoSource : NSObject
-
-/** The current state of the RTCVideoSource. */
-@property(nonatomic, readonly) RTCSourceState state;
+/*
+ * Creates a webrtc::VideoRendererInterface surface for an RTCVideoRenderer. The
+ * webrtc::VideoRendererInterface is used by WebRTC rendering code - this
+ * adapter adapts calls made to that interface to the RTCVideoRenderer supplied
+ * during construction.
+ */
+@interface RTCVideoRendererAdapter : NSObject
 
 - (instancetype)init NS_UNAVAILABLE;
 
 @end
 
 NS_ASSUME_NONNULL_END