Hide the `--web-renderer` option in the Flutter Tool. The defaults already cover all fully supported modes:
- `flutter build web` provides canvaskit + dart2js
- `flutter build web --wasm` provides skwasm + dart2wasm
We do not want to encourage production usage of any other permutations (e.g. `auto` or `html`), in particular those that simply do not work (e.g. `skwasm` + dart2js).
Fixes https://github.com/flutter/flutter/issues/140096
Fixes https://github.com/flutter/flutter/issues/151786