Now that the buckets are empty, we can delete the CloudFormation stacks:
Delete the CloudFormation stacks in following sequence and please wait for each to complete before going to next one.
Delete the sam-app stack
aws cloudformation delete-stack --stack-name sam-app
Delete the sam-app-cicd stack
aws cloudformation delete-stack --stack-name sam-app-cicd
Delete the aws-sam-cli-managed-default stack
aws cloudformation delete-stack --stack-name aws-sam-cli-managed-default