iOS: Remove (seemingly?) unneded `extern C` blocks that break build

platform/iphone/game_center.mm

@@ -32,21 +32,10 @@
 
 #include "game_center.h"
 
-#ifdef __IPHONE_9_0
-
-#import <GameKit/GameKit.h>
-extern "C" {
-
-#else
+#import "app_delegate.h"
 
-extern "C" {
 #import <GameKit/GameKit.h>
 
-#endif
-
-#import "app_delegate.h"
-};
-
 GameCenter *GameCenter::instance = NULL;
 
 void GameCenter::_bind_methods() {

platform/iphone/icloud.mm

@@ -32,18 +32,10 @@
 
 #include "icloud.h"
 
-#ifndef __IPHONE_9_0
-extern "C" {
-#endif
-
 #import "app_delegate.h"
 
 #import <Foundation/Foundation.h>
 
-#ifndef __IPHONE_9_0
-};
-#endif
-
 ICloud *ICloud::instance = NULL;
 
 void ICloud::_bind_methods() {

platform/iphone/in_app_store.mm

@@ -32,10 +32,8 @@
 
 #include "in_app_store.h"
 
-extern "C" {
 #import <Foundation/Foundation.h>
 #import <StoreKit/StoreKit.h>
-};
 
 bool auto_finish_transactions = true;
 NSMutableDictionary *pending_transactions = [NSMutableDictionary dictionary];