Don't pull in selinux-policy as a requires
    
    Building Fedora images without the selinux policy should be
    possible. Currently, out of the 500 packages or so installed in
    the mkosi-kernel fedora image (https://github.com/DaanDeMeyer/mkosi-kernel),
    libguestfs is the only one that has a requires on selinux-policy.
    Let's make sure we don't pull in selinux-policy but do keep the version
    requirement intact if it is already installed.