title: S3 bucket is not removed by CDK destroy
body: <p>For example, my CDK project has S3 bucket, IAM role, and Lambda function.</p>
  <pre><code>$ cdk bootstrap
  $ cdk deploy 
  </code></pre>
  <p>This creates an S3 bucket, IAM role, and Lambda function.</p>
  <pre><code>$ cdk destroy
  </code></pre>
  <p>It removes the IAM role and Lambda function but the S3 bucket is retained.</p>
  <p>Of course, the S3 bucket is empty.</p>
  <p>Is this the correct behavior? if so, which resources will be retained other than S3 buckets?</p>