PeerConnection(iOS): make ARC-clean talk/.../objc* and talk/examples/ios

- Removes a strong-reference cycle between RTCPeerConnection and
  RTCPeerConnectionObserver
- Gives RTCPeerConnectionObserver a virtual dtor
- Ensures RTCPeerConnectionTest tears down correctly
- Ensures AppRTCDemo tears down correctly

This is the talk/ half; the webrtc/ half is in https://webrtc-codereview.appspot.com/10539005

BUG=3054,3055,3100
R=noahric@google.com

Review URL: https://webrtc-codereview.appspot.com/10499005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5771 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/talk/examples/ios/AppRTCDemo/APPRTCViewController.m b/talk/examples/ios/AppRTCDemo/APPRTCViewController.m
index 8c5ccde..3cebb72 100644
--- a/talk/examples/ios/AppRTCDemo/APPRTCViewController.m
+++ b/talk/examples/ios/AppRTCDemo/APPRTCViewController.m
@@ -77,7 +77,7 @@
   [_remoteVideoView removeFromSuperview];
   self.remoteVideoView = nil;
 
-  [_remoteVideoView renderVideoTrackInterface:nil];
+  [_localVideoView renderVideoTrackInterface:nil];
   [_localVideoView removeFromSuperview];
   self.localVideoView = nil;
 }