Delete a policy.

        :type policy_name: str
        :param policy_name: The name or ARN of the policy to delete.

        :type autoscale_group: str
        :param autoscale_group: The name of the autoscale group.

def delete_policy(self, policy_name, autoscale_group=None):
        """
        Delete a policy.

        :type policy_name: str
        :param policy_name: The name or ARN of the policy to delete.

        :type autoscale_group: str
        :param autoscale_group: The name of the autoscale group.
        """
        params = {'PolicyName': policy_name}
        if autoscale_group:
            params['AutoScalingGroupName'] = autoscale_group
        return self.get_status('DeletePolicy', params)