setup.sh: GitHub needs HTTPS, GUB probably no longer needed

[karlinhigh]

From:

https://github.com/fedelibre/LilyDev/blob/master/mkosi/debian/mkosi.extra/etc/skel/setup.sh

I see another recent commit saying GitLab needed https:// instead of git:// downloads.

783767f

It looks like GitHub needs this as well now. The git:// URLs time out for git clone, while https:// works.

Also, GUB has been retired as a builder of LilyPond binaries, probably that repository is no longer needed?

[fedelibre]

Yes, GUB repository is no longer needed.

I don't have time nor motivation to maintain LilyDev. I don't even know if it's still used by anyone.