Revert of Split iOS sdk in to separate targets (patchset #13 id:280001 of https://codereview.webrtc.org/2862543002/ )

Reason for revert:
Breaking downstream projects.

Original issue's description:
> 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}
> Committed: 52c83fe710

TBR=magjed@webrtc.org,denicija@webrtc.org,tkchin@webrtc.org,henrika@webrtc.org,kthelgason@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:4867

Review-Url: https://codereview.webrtc.org/2890513002
Cr-Commit-Position: refs/heads/master@{#18170}

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

@@ -0,0 +1,49 @@
+/*
+ *  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/RTCDataChannel.h"
+
+#include "webrtc/api/datachannelinterface.h"
+#include "webrtc/base/scoped_ref_ptr.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RTCDataBuffer ()
+
+/**
+ * The native DataBuffer representation of this RTCDatabuffer object. This is
+ * needed to pass to the underlying C++ APIs.
+ */
+@property(nonatomic, readonly) const webrtc::DataBuffer *nativeDataBuffer;
+
+/** Initialize an RTCDataBuffer from a native DataBuffer. */
+- (instancetype)initWithNativeBuffer:(const webrtc::DataBuffer&)nativeBuffer;
+
+@end
+
+
+@interface RTCDataChannel ()
+
+/** Initialize an RTCDataChannel from a native DataChannelInterface. */
+- (instancetype)initWithNativeDataChannel:
+    (rtc::scoped_refptr<webrtc::DataChannelInterface>)nativeDataChannel
+    NS_DESIGNATED_INITIALIZER;
+
++ (webrtc::DataChannelInterface::DataState)
+    nativeDataChannelStateForState:(RTCDataChannelState)state;
+
++ (RTCDataChannelState)dataChannelStateForNativeState:
+    (webrtc::DataChannelInterface::DataState)nativeState;
+
++ (NSString *)stringForState:(RTCDataChannelState)state;
+
+@end
+
+NS_ASSUME_NONNULL_END