circleci.go
func (c *Client) DeleteEnvVar(account, repo, name string) error {
	return c.request("DELETE", fmt.Sprintf("project/%s/%s/envvar/%s", account, repo, name), nil, nil, nil)
}
func (c *Client) DeleteEnvVar(account, repo, name string) error {
	return c.request("DELETE", fmt.Sprintf("project/%s/%s/envvar/%s", account, repo, name), nil, nil, nil)
}
// DeleteEnvVar deletes the specified environment variable from the project