prow/github/client.go
func (c *Client) DeleteRepoLabel(org, repo, label string) error {
	c.log("DeleteRepoLabel", org, repo, label)
	_, err := c.request(&request{
		method:      http.MethodDelete,
		accept:      "application/vnd.github.symmetra-preview+json", // allow the description field -- https://developer.github.com/changes/2018-02-22-label-description-search-preview/
		path:        fmt.Sprintf("/repos/%s/%s/labels/%s", org, repo, label),
		requestBody: Label{Name: label},
		exitCodes:   []int{204},
	}, nil)
	return err
}
func (c *Client) DeleteRepoLabel(org, repo, label string) error {
	c.log("DeleteRepoLabel", org, repo, label)
	_, err := c.request(&request{
		method:      http.MethodDelete,
		accept:      "application/vnd.github.symmetra-preview+json", // allow the description field -- https://developer.github.com/changes/2018-02-22-label-description-search-preview/
		path:        fmt.Sprintf("/repos/%s/%s/labels/%s", org, repo, label),
		requestBody: Label{Name: label},
		exitCodes:   []int{204},
	}, nil)
	return err
}
// DeleteRepoLabel deletes a label in org/repo
//
// See https://developer.github.com/v3/issues/labels/#delete-a-label