Use the FailedStorage instead

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

apps/files_external/lib/Lib/Backend/InvalidBackend.php

@@ -40,7 +40,7 @@ class InvalidBackend extends Backend {
 		$this->invalidId = $invalidId;
 		$this
 			->setIdentifier($invalidId)
-			->setStorageClass('\OCA\Files_External\Lib\Storage\InvalidStorage')
+			->setStorageClass('\OC\Files\Storage\FailedStorage')
 			->setText('Unknown storage backend ' . $invalidId)
 		;
 	}

apps/files_external/lib/Lib/Storage/InvalidStorage.php

@@ -1,30 +0,0 @@
-<?php
-/**
- * @author Vincent Petry <pvince81@owncloud.com>
- *
- * @copyright Copyright (c) 2016, ownCloud GmbH.
- * @license AGPL-3.0
- *
- * This code is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Affero General Public License, version 3,
- * as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU Affero General Public License for more details.
- *
- * You should have received a copy of the GNU Affero General Public License, version 3,
- * along with this program.  If not, see <http://www.gnu.org/licenses/>
- *
- */
-
-namespace OCA\Files_External\Lib\Storage;
-
-use OCP\Files\StorageNotAvailableException;
-
-class InvalidStorage {
-	public function __construct($params) {
-		throw new StorageNotAvailableException();
-	}
-}