func (c *Client) UnrequestReview(org, repo string, number int, logins []string) error {
	c.log("UnrequestReview", org, repo, number, logins)
	var pr PullRequest
	body, err := prepareReviewersBody(logins, org)
	if len(body) == 0 {
		// No point in doing request for none,
		// if some logins didn't make it to body, extras.Users will catch them.
		return err
	}
	_, err = c.request(&request{
		method:      http.MethodDelete,
		path:        fmt.Sprintf("/repos/%s/%s/pulls/%d/requested_reviewers", org, repo, number),
		accept:      "application/vnd.github.symmetra-preview+json",
		requestBody: body,
		exitCodes:   []int{http.StatusOK /*200*/},
	}, &pr)
	if err != nil {
		return err
	}
	extras := ExtraUsers{action: "remove the PR review request for"}
	for _, user := range pr.RequestedReviewers {
		found := false
		for _, toDelete := range logins {
			if NormLogin(user.Login) == NormLogin(toDelete) {
				found = true
				break
			}
		}
		if found {
			extras.Users = append(extras.Users, user.Login)
		}
	}
	if len(extras.Users) > 0 {
		return extras
	}
	return nil
}
func (c *Client) UnrequestReview(org, repo string, number int, logins []string) error {
	c.log("UnrequestReview", org, repo, number, logins)
	var pr PullRequest
	body, err := prepareReviewersBody(logins, org)
	if len(body) == 0 {
		// No point in doing request for none,
		// if some logins didn't make it to body, extras.Users will catch them.
		return err
	}
	_, err = c.request(&request{
		method:      http.MethodDelete,
		path:        fmt.Sprintf("/repos/%s/%s/pulls/%d/requested_reviewers", org, repo, number),
		accept:      "application/vnd.github.symmetra-preview+json",
		requestBody: body,
		exitCodes:   []int{http.StatusOK /*200*/},
	}, &pr)
	if err != nil {
		return err
	}
	extras := ExtraUsers{action: "remove the PR review request for"}
	for _, user := range pr.RequestedReviewers {
		found := false
		for _, toDelete := range logins {
			if NormLogin(user.Login) == NormLogin(toDelete) {
				found = true
				break
			}
		}
		if found {
			extras.Users = append(extras.Users, user.Login)
		}
	}
	if len(extras.Users) > 0 {
		return extras
	}
	return nil
}
// UnrequestReview tries to remove the users listed in 'logins' from the requested reviewers of the
// specified PR. The GitHub API treats deletions of review requests differently than creations. Specifically, if
// 'logins' contains a user that isn't a requested reviewer, other users that are valid are still removed.
// Furthermore, the API response lists the set of requested reviewers after the deletion (unlike request creations),
// so we can determine if each deletion was successful.
// The API responds with http status code 200 no matter what the content of 'logins' is.
//
// See https://developer.github.com/v3/pulls/review_requests/#delete-a-review-request