private void untrack(BrokerHeartbeatState broker) {
        if (!broker.fenced()) {
            unfenced.remove(broker);
            if (!broker.shuttingDown()) {
                active.remove(broker);
            }
        }
    }
Stop tracking the broker in the unfenced list and active set, if it was tracked
in either of these.

@param broker        The broker state to stop tracking.
metadata/src/main/java/org/apache/kafka/controller/BrokerHeartbeatManager.java