Build dynamic iOS SDK.

- Places most ObjC code into webrtc/sdk/objc instead.
- New gyp targets to build, strip and export symbols for dylib.
- Removes old script used to generate dylib.

BUG=

Review URL: https://codereview.webrtc.org/1903663002

Cr-Commit-Position: refs/heads/master@{#12524}
diff --git a/webrtc/examples/objc/AppRTCDemo/ARDWebSocketChannel.m b/webrtc/examples/objc/AppRTCDemo/ARDWebSocketChannel.m
index 0e753e8..87a690e 100644
--- a/webrtc/examples/objc/AppRTCDemo/ARDWebSocketChannel.m
+++ b/webrtc/examples/objc/AppRTCDemo/ARDWebSocketChannel.m
@@ -10,7 +10,7 @@
 
 #import "ARDWebSocketChannel.h"
 
-#import "webrtc/base/objc/RTCLogging.h"
+#import "WebRTC/RTCLogging.h"
 #import "SRWebSocket.h"
 
 #import "ARDSignalingMessage.h"