Switch to per variant fedora-release-* package
    
    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.