code: func (s *IssuesService) RemoveLabelForIssue(ctx context.Context, owner string, repo string, number int, label string) (*Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/issues/%d/labels/%v", owner, repo, number, label)
  	req, err := s.client.NewRequest("DELETE", u, nil)
  	if err != nil {
  		return nil, err
  	}
  
  	// TODO: remove custom Accept header when this API fully launches.
  	req.Header.Set("Accept", mediaTypeLabelDescriptionSearchPreview)
  
  	return s.client.Do(ctx, req, nil)
  }
docs: // RemoveLabelForIssue removes a label for an issue.
  //
  // GitHub API docs: https://developer.github.com/v3/issues/labels/#remove-a-label-from-an-issue