Split iOS sdk in to separate targets

This CL splits the iOS sdk into separate static libraries for video,
audio, ui, common, and peerconnection-related code. This will in the
future make it easier to compile WebRTC without unneeded components.

BUG=webrtc:4867

Review-Url: https://codereview.webrtc.org/2862543002
Cr-Commit-Position: refs/heads/master@{#18166}

webrtc/sdk/objc/Framework/Classes/RTCAVFoundationVideoSource+Private.h

@@ -1,27 +0,0 @@
-/*
- *  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 "WebRTC/RTCAVFoundationVideoSource.h"
-
-#include "avfoundationvideocapturer.h"
-
-NS_ASSUME_NONNULL_BEGIN
-
-@interface RTCAVFoundationVideoSource ()
-
-@property(nonatomic, readonly) webrtc::AVFoundationVideoCapturer *capturer;
-
-/** Initialize an RTCAVFoundationVideoSource with constraints. */
-- (instancetype)initWithFactory:(RTCPeerConnectionFactory *)factory
-                    constraints:(nullable RTCMediaConstraints *)constraints;
-
-@end
-
-NS_ASSUME_NONNULL_END