code: def remove_async_sns_topic(self, lambda_name):
          
          topic_name = get_topic_name(lambda_name)
          removed_arns = []
          for sub in self.sns_client.list_subscriptions()['Subscriptions']:
              if topic_name in sub['TopicArn']:
                  self.sns_client.delete_topic(TopicArn=sub['TopicArn'])
                  removed_arns.append(sub['TopicArn'])
          return removed_arns
docs: Remove the async SNS topic.