code: public Set<ClusterNode.GrantId> deleteNode(String nodeName) {
      ClusterNode node = nameToNode.get(nodeName);
      if (node == null) {
        LOG.warn("Trying to delete non-existent node: " + nodeName);
        return null;
      }
      return deleteNode(node);
    }
docs: Delete the node from the cluster. This happens when the node times out
  or is being decommissioned.
  @param nodeName the name of the node to remove
  @return the list of grants that are running on the node