I think that doesn't actually remove you from the GitHub contributors list. I had used the wrong identity for a commit and tried all manners of git manipulation and force push, but GitHub kept me on the list. In the end I just nuked that account.
Ah, I didn't think of it at all, I was only thinking about a hypothetical responsibility of whoever is in charge of the git repository, not the extra github flavoring.
Edit: Apparently renaming branches and reverting that works: https://stackoverflow.com/a/69294044