Remove dead code for system VK.

ui/keyboard/resources/elements/kb-altkey-container.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-altkey-container', {
-  resetActiveElement: function() {
-    var activeAccentKeySet = this.querySelector('#' + this.keyset);
-    var offset = activeAccentKeySet.offset;
-    var element = activeAccentKeySet.firstElementChild;
-    while (offset) {
-      element = element.nextElementSibling;
-      offset--;
-    }
-    element.classList.add('active');
-  },
-  up: function(detail) {
-    this.hidden = true;
-    this.resetActiveElement();
-    this.keyset = null;
-  },
-  out: function(event) {
-    // Check if touch is outside container boundaries.
-    if(!(this.compareDocumentPosition(event.relatedTarget)
-        & Node.DOCUMENT_POSITION_CONTAINED_BY)) {
-      this.hidden = true;
-    }
-  },
-
-  hiddenChanged: function() {
-    this.fire('stateChange', {
-      state: 'candidatePopupVisibility',
-      value: !!this.hidden
-    });
-  },
-});