References:
        https://developer.github.com/v3/issues/labels/#remove-a-label-from-an-issue

def remove_label_from_pr(repo: GithubRepository,
                         pull_id: int,
                         label: str) -> bool:
    """
    References:
        https://developer.github.com/v3/issues/labels/#remove-a-label-from-an-issue
    """
    url = ("https://api.github.com/repos/{}/{}/issues/{}/labels/{}"
           "?access_token={}".format(repo.organization,
                                     repo.name,
                                     pull_id,
                                     label,
                                     repo.access_token))
    response = requests.delete(url)

    if response.status_code == 404:
        payload = json.JSONDecoder().decode(response.content.decode())
        if payload['message'] == 'Label does not exist':
            return False

    if response.status_code == 200:
        # Removed the label.
        return True

    raise RuntimeError(
        'Label remove failed. Code: {}. Content: {}.'.format(
            response.status_code, response.content))