Remove dead code for system VK.

ui/keyboard/resources/layouts/symbol-altkeys.js

-// Copyright 2013 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.
-
-var symbolAltKeys = {
-  '1': ['\u00B9', // HintText 1
-        '\u00BD', // Vulgar fraction 1/2
-        '\u2153', // Vulgar fraction 1/3
-        '\u00BC', // Vulgar fraction 1/4
-        '\u215B'], // Vulgar fraction 1/8
-  '2': ['\u00B2', // HintText 2
-        '\u2154'], // Vulgar fraction 2/3
-  '3': ['\u00B3', // HintText 3
-        '\u00BE', // Vulgar fraction 3/4
-        '\u215C'], // Vulgar fraction 3/8
-  '4': ['\u2074'], // HintText 4
-  '5': ['\u215D'], // Vulgar fraction 5/8
-  '7': ['\u215E'], // Vulgar fraction 7/8
-  '0': ['\u00D8', // Empty set
-        '\u207F'], // HintText small n
-  '$': ['\u20AC', // Euro sign
-        '\u00A5', // Yen sign
-        '\u00A3', // Pound sign
-        '\u00A2'], // Cent sign
-  '%': ['\u2030'], // Per Mille sign
-  '*': ['\u2605', // Black star
-        '\u2020', // Dagger
-        '\u2021'], // Double dagger
-  '\\': ['/'],
-  '"': ['\u201C', // Left double quote
-        '\u201D', // Right double quote
-        '\u201E', // Double low-9 quotation mark
-        '\u00AB', // Left double angle quote
-        '\u00BB'], // Right double angle quote
-  '-': ['_'],
-  '!': ['\u00A1'], // Inverted exclamation mark
-  '?': ['\u00BF'], // Inverted question mark
-  '(': ['<', '{', '['],
-  ')': ['>', '}', ']'],
-  '.com' : ['.net','.org','.gov']
-};
-
-document.addEventListener('polymer-ready', function() {
-  var altkeyMetadata = document.createElement('kb-altkey-data');
-  altkeyMetadata.registerAltkeys(symbolAltKeys);
-});