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