code: protected function removeIdentityCookie()
      {
          Yii::$app->getResponse()->getCookies()->remove(Yii::createObject(array_merge($this->identityCookie, [
              'class' => 'yii\web\Cookie',
          ])));
      }
docs: Removes the identity cookie.
  This method is used when [[enableAutoLogin]] is true.
  @since 2.0.9