[FlUtTeR] debug 베너 없애기

출처 : https://blog.wonhada.com/?p=3506

class MainApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return CupertinoApp(

      debugShowCheckedModeBanner: false, // Debug 배너 제거
      ...
    );
  }
}

debugShowCheckedModeBanner: false