Instead of taking the metadata from PackageKit-cached-metadata package
as we were doing previously, copy it over directly during the compose
from https://kojipkgs.fedoraproject.org/mash/
This makes it much less error prone as we always get the very latest
metadata, and makes maintenance much simpler as we don't need to roll
PackageKit-cached-metadata by hand. Users are also going to appreciate
this because it makes post-GA updates smaller as they won't have to
download updates for the PackageKit-cached-metadata subpackage each time
PackageKit gets updated.
The gnome-settings-daemon updates plugin is gone and update downloading
is handled by gnome-software instead. Adapt the live image schema
overrides for the changes.
