Tidy up the Fedora mkosi Package list

Tidy up the Fedora mkosi Package list

libzstd is a new dependency for systemd that's not in a stable release
yet, so it's not pulled in by the RPM package dependency. Manually
include it in the package section so the image mkosi produces works. It
can be removed when the RPM depends on it.

Additionally, a number of packages in the list appear to be pulled in
because they're dependencies in the systemd rpm, so remove them.
Finally, mkosi v5 adds the proper fs utilities for bootable images type
so drop that dependency as well.