void decrementUpdated(String host, int port, UpdateType updateType) {
    updateHelpers.computeIfAbsent(updateType, type -> new Helper(numberOfReplicas)).decrementCount(host, port);
  }
Nullifies the update notification for {@code updateType} on {@code host}:{@code port}.
This method is NOT thread safe and should not be used concurrently with other methods in this class like
await() and track().
@param host the host that to decrement on
@param port the port of the host that describes the instance along with {@code host}.
@param updateType the {@link UpdateType} to nullify the notification for
ambry-test-utils/src/main/java/com/github/ambry/server/MockCluster.java