This request is legitimate. The issue was reported by not someone an admin, so it was impossible to know that before. Asking for deletion of commits from public repositoriies should always been seen as an extreme solution to a problem, and ideally avoided at all costs.
The issue is not with the contents of the commit, but that the signature is considered invalid by Guix. Guix cannot safely pull from the repository until it is reverted. That sounds like a technical issue with Guix, there are now two more commits on guix/maintaince master. You're asking for doing something very destructive to the repostiroy, including anyone who has a checkout of this will get affected. I think this request should be declined, if Guix cannot manage this it should be fixed there.
