Move the fedora-release-* package requirement to each variant treefile
to enable per variant specifc release package. Silverblue keeps its
existing release package and Kinoite gets its own for Fedora 35:
https://fedoraproject.org/wiki/Changes/Fedora_Kinoite
For now, all other unofficial variants will use the Fedora generic
release package (or the corresponding Spin release package) with the
ostree counting and desktop sub packages to enable those features by
default.
