code: public function run($id)
      {
          $model = $this->controller->findModel($id);
          if ($model->is_system) {
              \Yii::$app->session->setFlash('warning', \Yii::t('app', 'You cannot update or delete system handlers'));
          } else {
              $model->delete();
          }
          return $this->controller->redirect(['index']);
      }
docs: Deletes an existing EventEventHandler model.
  If deletion is successful, the browser will be redirected to the 'index' page.
  @param integer $id
  @return mixed