_live_build: workaround util-linux-user problem for KDE live
    
    util-linux-user subpackage was removed but comps wasn't updated.
    I've fixed comps now, but that won't "kick in" until after the
    next Rawhide compose; we need to workaround the issue until then.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>