pdc_update_critpath: Drop all the yum-related code
    
    Since toddlers are running on Fedora where yum is not available there is
    not point in keeping this code around.
    
    That being said, having it in git may be useful if we ever need to dig it
    out.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>