Remove dead code for system VK.

ui/keyboard/resources/elements/kb-altkey.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.
-
-/**
- * Filter out mouse/touch movements internal to this node. When moving
- * inside a node, the event should be filter out.
- * @param {Node} node The accent key node which receives event.
- * @param {event} event A pointer move event.
- * @return {boolean} True if event is external to node.
- */
- function isRelevantEvent(node, event) {
-  return !(node.compareDocumentPosition(event.relatedTarget)
-    & Node.DOCUMENT_POSITION_CONTAINED_BY);
-};
-Polymer('kb-altkey', {
-  over: function(event) {
-    if (isRelevantEvent(this, event)) {
-      // Dragging over an accent key is equivalent to pressing on the accent
-      // key.
-      this.fire('key-down', {});
-    }
-  },
-
-  out: function(event) {
-    if (isRelevantEvent(this, event)) {
-      this.classList.remove('active');
-    }
-  },
-
-  up: function(event) {
-    var detail = {
-      char: this.charValue
-    };
-    this.fire('key-up', detail);
-  },
-
-  // TODO(bshe): kb-altkey should extend from kb-key-base.
-  autoRelease: function() {
-  },
-
-  /**
-   * Character value associated with the key. Typically, the value is a
-   * single character, but may be multi-character in cases like a ".com"
-   * button.
-   * @return {string}
-   */
-   get charValue() {
-    return this.char || this.textContent;
-  }
-});
-