Removed unnecessary inheritance

Summary: Quick code cleaning - Facebook class doesn't need to inherit from
FBRequestDelegate.

Test Plan: Check if it compiles and login in / login out works.

Reviewers: yariv

Reviewed By: yariv

CC: jgabbard, yariv

Differential Revision: 380359

src/Facebook.h

@@ -25,7 +25,7 @@
  * and Graph APIs, and start user interface interactions (such as
  * pop-ups promoting for credentials, permissions, stream posts, etc.)
  */
-@interface Facebook : NSObject<FBLoginDialogDelegate, FBRequestDelegate>{
+@interface Facebook : NSObject<FBLoginDialogDelegate>{
   NSString* _accessToken;
   NSDate* _expirationDate;
   id<FBSessionDelegate> _sessionDelegate;