code: public CompletableFuture<Void> deleteSubscriptionAsync(String topicPath, String subscriptionName) {
          EntityNameHelper.checkValidTopicName(topicPath);
          EntityNameHelper.checkValidSubscriptionName(subscriptionName);
          String path = EntityNameHelper.formatSubscriptionPath(topicPath, subscriptionName);
          return deleteEntityAsync(path);
      }
docs: Deletes the subscription described by the topicPath and the subscriptionName.
  @param topicPath - The name of the topic.
  @param subscriptionName - The name of the subscription.
  @return A completable future that completes when the subscription is deleted.
  @throws IllegalArgumentException - path is not null / empty / too long / invalid.