I have made improvements and bug fixes to ppa-purge (long ago), but they have not been merged, see here. My branch is here. I wonder, if it was best to fork and rename the project, as the usage is a bit different and it can "purge" more than just PPAs. Maybe this is something that 'sudo add-apt-repository --remove' should be able to do. Currently add-apt-repository can't even add a repository (https://askubuntu.com/q/1147032/21005).