Server: don't require rolekit (not installable, soon to be retired)
    
    rolekit has not been ported to Python 3.7 and will be retired
    instead (per @sgallagh). We must drop this dependency as it
    prevents fedora-release-server being installed (instead anaconda
    silently drops it, so a 'Server' install completes but is not
    really 'Server' in several ways).
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>