Remove a node registration from a directory service.

     DEREGISTER [DECNET] NODE node-id
         [ DIRECTORY_SERVICE dir-service ]
         [ PHASEIV_PREFIX addr-prefix ]
         [ REVERSE_DIRECTORY rev-dir-name ]
         [ SYNONYM_DIRECTORY syn-dir-name ]

 This is used when a node is no longer available in the network, and the
 node registration needs to be removed from a directory service.