Deletes a DB security group.Show details from next link. https://docs.aws.amazon.com/ja_jp/cli/latest/reference/rds/delete-db-security-group.html
| aws rds delete-db-security-group --db-security-group-name |
| postgresql - Amazon RDS: Why is Security Groups listed twice? - Server Fault : http://serverfault.com/questions/827189/amazon-rds-why-is-security-groups-listed-twice |