@Override
  public synchronized boolean removeAccountUpdateConsumer(Consumer<Collection<Account>> accountUpdateConsumer) {
    Objects.requireNonNull(accountUpdateConsumer, "accountUpdateConsumer to unsubscribe cannot be null");
    return accountUpdateConsumers.remove(accountUpdateConsumer);
  }
Constructor.
@param shouldReturnOnlyUnknown {@code true} if always returns {@link InMemAccountService#UNKNOWN_ACCOUNT} when queried
                                                    by account name; {@code false} to do the actual query.
@param notifyConsumers {@code true} if consumers should be notified of account changes. {@code false} otherwise.
ambry-test-utils/src/main/java/com/github/ambry/account/InMemAccountService.java