'Deletes a DB subnet group.
The specified database subnet group must not be associated
with any DB instances.
:type db_subnet_group_name: string
:param db_subnet_group_name:
The name of the database subnet group to delete.
You cannot delete the default subnet group.
Constraints:
+ Must be 1 to 255 alphanumeric characters
+ First character must be a letter
+ Cannot end with a hyphen or contain two consecutive hyphens'

def delete_db_subnet_group(self, db_subnet_group_name):

    params = {'DBSubnetGroupName': db_subnet_group_name}
    return self._make_request(action='DeleteDBSubnetGroup', verb='POST', path='/', params=params)
