Remove unused bootstrap images
Bootstrap images for 9.2/9.4/9.6 can be dropped, we only use 9.8/9.10 in ghc ci now.
Due to a large amount of spam we do not allow new users to create repositories, they are "external" users. If you are a new user and want to create a repository, for example for forking GHC, open a new issue on ghc/ghc using the "get-verified" issue template
Bootstrap images for 9.2/9.4/9.6 can be dropped, we only use 9.8/9.10 in ghc ci now.