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 are kept on the Silverblue
    release package until we create a generic brand for rpm-ostree based
    versions of Fedora.