Fixed ThemeData in the Flutter Samples unnecessarily includes useMaterial3 = true (Issue #2214) (#2217)

flutter_maps_firestore/lib/main.dart

@@ -36,7 +36,6 @@ class App extends StatelessWidget {
       theme: ThemeData(
         colorSchemeSeed: Colors.pink,
         scaffoldBackgroundColor: Colors.pink[50],
-        useMaterial3: true,
       ),
     );
   }