[iOS Example] Move protocol conformance declaration out of header

This can just be in the class extension in the implementation file.

Author: jonathandann

Peertalk iOS Example/PTViewController.h

@@ -1,6 +1,6 @@
 #import <UIKit/UIKit.h>
 #import "PTChannel.h"
 
-@interface PTViewController : UIViewController <PTChannelDelegate, UITextFieldDelegate>
+@interface PTViewController : UIViewController
 
 @end

Peertalk iOS Example/PTViewController.m

@@ -1,7 +1,10 @@
 #import "PTExampleProtocol.h"
 #import "PTViewController.h"
 
-@interface PTViewController () {
+@interface PTViewController () <
+PTChannelDelegate,
+UITextFieldDelegate
+> {
   __weak PTChannel *serverChannel_;
   __weak PTChannel *peerChannel_;
 }