synchronized void decrementUpdatedReplica(String blobId, String host, int port, UpdateType updateType) {
    objectTracker.get(blobId).decrementDeleted(host, port);
  }
Nullifies the update notification of type {@code updateType} for {@code blobId} on {@code host}:{@code port}.
This method should not be used concurrently with the await functions
@param blobId the blob ID whose update notification needs to be nullified
@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/MockNotificationSystem.java