Drop cupertino_store (#2162)

## Pre-launch Checklist

- [x] I read the [Effective Dart: Style] _recently_, and have followed
its advice.
- [x] I signed the [CLA].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Effective Dart: Style]:
https://dart.dev/guides/language/effective-dart/style
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat

README.md

@@ -11,8 +11,7 @@ Here is a list of the codelabs represented here:
   - [Adding Google Maps to a Flutter app](https://codelabs.developers.google.com/codelabs/google-maps-in-flutter) is in [`google-maps-in-flutter`](google-maps-in-flutter)
   - [Adding in-app purchases to your Flutter app](https://codelabs.developers.google.com/codelabs/flutter-in-app-purchases) is in [`in_app_purchases`](in_app_purchases)
   - [Adding WebView to your Flutter app](https://codelabs.developers.google.com/codelabs/flutter-webview) is in [`webview_flutter`](webview_flutter)
-  - [Building a board game with TensorFlow Agents and Flutter](https://codelabs.developers.google.com/tfagents-flutter) is in [`tfagents-flutter`](tfagents-flutter)  
-  - [Building a Cupertino app with Flutter](https://codelabs.developers.google.com/codelabs/flutter-cupertino) is in [`cupertino_store`](cupertino_store)
+  - [Building a board game with TensorFlow Agents and Flutter](https://codelabs.developers.google.com/tfagents-flutter) is in [`tfagents-flutter`](tfagents-flutter)
   - [Building a full-stack movie recommendation system](https://codelabs.developers.google.com/tfrecommenders-flutter) is in [`tfrs-flutter`](tfrs-flutter)
   - [Building an animated responsive app layout with Material 3](https://codelabs.developers.google.com/codelabs/flutter-animated-responsive-layout) is in [`animated-responsive-layout`](animated-responsive-layout)
   - [Building next generation UIs in Flutter](https://codelabs.developers.google.com/codelabs/flutter-next-gen-uis?hl=en#0) is in [`next-gen-ui`](next-gen-ui)