Remove dead code for system VK.

ui/keyboard/resources/elements/kb-key-import.js

-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-Polymer('kb-key-import', {
-  /**
-  * The id of the document fragment that will be imported.
-   */
-  importId: null,
-
-  /**
-   * Import content from a document fragment.
-   * @param {!DocumentFragment} content Document fragment that contains
-   *     the content to import.
-   */
-  importDoc: function(content) {
-    var id = this.getAttribute('importId');
-    var fragment = content.querySelector('#' + id);
-    return fragment && fragment.content ? fragment.content : fragment;
-  }
-});
-