Stop requesting anonymous keytab and purge all references of it
    
    anonymous kinit using keytab never worked so we may safely remove all
    code that requests/uses it.
    
    https://pagure.io/freeipa/issue/6830
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Simo Sorce <ssorce@redhat.com>