scripts: setup-user: drop unneeded groups. (from Mobian)

[eugenr]

https://salsa.debian.org/Mobian-team/mobian-recipes/-/commit/c8584bc73378c2d8677ca42fd9beb01f2c9f9817

See that commit where Mobian considers some groups unneeded and stops adding the user to them. We took the script from them and maybe we should apply that change too.

Mobian's issue on that was: https://salsa.debian.org/Mobian-team/mobian-recipes/-/issues/28

I've just seen that change in Mobian, maybe someone can take that commit and apply it here. And test it...