[MD extensions] removed unused I18nBehavior(s)

This CL removes a couple instance of I18nBehavior being declared by not
being used.

(code health)

Bug: None
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ic779231d1cd33d02216a8c7b4bf48e9de33cb62d
Reviewed-on: https://chromium-review.googlesource.com/820457Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Dave Schuyler <dschuyler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523290}

chrome/browser/resources/md_extensions/compiled_resources2.gyp

@@ -221,7 +221,6 @@
       'dependencies': [
         '<(DEPTH)/ui/webui/resources/js/compiled_resources2.gyp:assert',
         '<(DEPTH)/ui/webui/resources/js/compiled_resources2.gyp:cr',
-        '<(DEPTH)/ui/webui/resources/js/compiled_resources2.gyp:i18n_behavior',
         '<(EXTERNS_GYP):developer_private',
         'shortcut_util',
       ],
@@ -248,7 +247,6 @@
       'target_name': 'toolbar',
       'dependencies': [
         '<(DEPTH)/ui/webui/resources/js/compiled_resources2.gyp:cr',
-        '<(DEPTH)/ui/webui/resources/js/compiled_resources2.gyp:i18n_behavior',
       ],
       'includes': ['../../../../third_party/closure_compiler/compile_js2.gypi'],
     },

chrome/browser/resources/md_extensions/shortcut_input.js

@@ -17,8 +17,6 @@ cr.define('extensions', function() {
   const ShortcutInput = Polymer({
     is: 'extensions-shortcut-input',
 
-    behaviors: [I18nBehavior],
-
     properties: {
       /** @type {!Object} */
       delegate: Object,

chrome/browser/resources/md_extensions/toolbar.js

@@ -26,8 +26,6 @@ cr.define('extensions', function() {
   const Toolbar = Polymer({
     is: 'extensions-toolbar',
 
-    behaviors: [I18nBehavior],
-
     properties: {
       /** @type {extensions.ToolbarDelegate} */
       delegate: Object,