/**
  * Removes users from the project (two-way unlink)
  * @param string $projectId
  * @param string $joinRequestId
  * @return string $projectId
  */
 public static function removeJoinRequest($projectId, $joinRequestId)
 {
     $project = new ProjectModel($projectId);
     $project->removeUserJoinRequest($joinRequestId);
     return $project->write();
 }