Add tool for removing tape

Let's be real. If developers realize that tape is not the right tool for the job, we want to support them too. It would be great if there was a `tapegen remove` command (or something similar) that

- [ ] removes all tape annotations from all classes
- [ ] removes the `tape.dart` file
- [ ] removes the `initializeTape()` call from `main`
- [ ] removes imports of `package:tape/tape.dart`
- [ ] removes tape from `dependencies` as well as taped-packages
- [ ] removes tapegen from `dev_dependencies`
- [ ] if there's no other dev dependency apart from `build_runner`, remove that too.

Start by tracing the existing tapegen commands and how they modify tape.dart, main, imports, and pubspec dependencies. Define the remove command around each checklist item, including taped-packages and the build_runner exception. Done means all listed tape artifacts are removed without deleting unrelated dependencies.

Written by the indexing model from the issue text.