Drop firmware-addon-dell from comps (#1561768)
    
    firmware-addon-dell is currently uninstallable and FTBFS in F28
    and Rawhide. I also suspect that it may be a dead and useless
    package - see https://bugzilla.redhat.com/show_bug.cgi?id=1555752
    (the FTBFS bug).
    
    Until that can all be resolved, at least, let's drop it from
    comps. It is currently getting pulled into the Server DVD, which
    is technically a release-blocking issue as long as it is not
    installable.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>