@Override
    protected void expire(List<Node> expired) {
        nodeRepository().nodes().performOn(NodeList.copyOf(expired),
                                           (node, lock) -> { nodeRepository().nodes().forget(node); return node; });
    }
This removes hosts from {@link com.yahoo.vespa.hosted.provision.Node.State#deprovisioned}, in dynamically provisioned
zones, after a grace period.

@author mpolden
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/DeprovisionedExpirer.java