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/RTCMetricsSampleInfo+Private.h

@@ -1,28 +0,0 @@
-/*
- *  Copyright 2016 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/RTCMetricsSampleInfo.h"
-
-// Adding 'nogncheck' to disable the gn include headers check.
-// We don't want to depend on 'system_wrappers:metrics_default' because
-// clients should be able to provide their own implementation.
-#include "webrtc/system_wrappers/include/metrics_default.h"  // nogncheck
-
-NS_ASSUME_NONNULL_BEGIN
-
-@interface RTCMetricsSampleInfo ()
-
-/** Initialize an RTCMetricsSampleInfo object from native SampleInfo. */
-- (instancetype)initWithNativeSampleInfo:
-    (const webrtc::metrics::SampleInfo &)info;
-
-@end
-
-NS_ASSUME_NONNULL_END