feat: remove app_provider, refactoring post_gen.dart

Author: DemeoStep

bricks/flutter_clean_base/__brick__/{{project_name.snakeCase()}}/lib/core/di/riverpod.dart

@@ -5,13 +5,5 @@ import 'package:{{project_name}}/app/riverpod/app_provider_imports.dart';
 //{imports end}
 
 void registerRiverpod(GetIt getIt) {
-  getIt.registerSingleton<StateNotifierProvider<AppProvider, AppState>>(
-    StateNotifierProvider<AppProvider, AppState>(
-      (ref) => AppProvider(),
-    ),
-  );
   //{riverpod end}
 }
-
-StateNotifierProvider<AppProvider, AppState> appProvider() =>
-    GetIt.I.get<StateNotifierProvider<AppProvider, AppState>>();