Fix build issue for the new app template (facebook#32772)

Summary:
Pull Request resolved: facebook#32772

Changelog: [internal] Fix a build issue for the new app template.

Reviewed By: philIip

Differential Revision: D33154125

fbshipit-source-id: ae696aeae6aac31678fe43a8963aab05c67c05d7

Author: sota000

template/ios/HelloWorld/AppDelegate.mm

@@ -25,8 +25,6 @@ @interface AppDelegate () <RCTCxxBridgeDelegate, RCTTurboModuleManagerDelegate>
 @end
 #endif
 
-using namespace facebook::react;
-
 @implementation AppDelegate
 
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions