Delete all old closed issues

Issues should not be synchronized between Github and Gitlab. That's not something I need. There are ~400 issues duplicated. I could turn off issues here, but I want people to also be able to open issues here. I also could delete them manually but it's too many clicks for all the issues. I managed to close them all using bulk edit, so it's already ok. But if the Python API for Gitlab allows to delete also them, I'll try if I have a minute. Very low priority though.