Update scripts based on recent configlet changes

I noticed in the recent PR #295, that our [`check_formatting`](https://github.com/exercism/dart/blob/main/bin/check_formatting.dart) is running `configlet lint` manually, which is no longer required since #283 added a separate workflow for it.

The following scripts need to be updated:

- ~~[`check_formatting`](https://github.com/exercism/dart/blob/main/bin/check_formatting.dart)~~

- [`create_exercise`](https://github.com/exercism/dart/blob/main/bin/create_exercise.dart)
- Will likely be replaced by a new generator used for all tracks with an plugin/extension for the dart track.

- [`presubmit`](https://github.com/exercism/dart/blob/main/bin/presubmit.dart) also needs an update.
> `configlet fmt` is not supported at the moment. Maybe later

> _Originally posted by @ErikSchierboom in https://github.com/exercism/dart/issues/301#issuecomment-781383216_