refactor Wikis class to ES module syntax

app/assets/javascripts/dispatcher.js

@@ -53,6 +53,7 @@ import UsersSelect from './users_select';
 import RefSelectDropdown from './ref_select_dropdown';
 import GfmAutoComplete from './gfm_auto_complete';
 import ShortcutsBlob from './shortcuts_blob';
+import Wikis from './wikis';
 import ZenMode from './zen_mode';
 import initSettingsPanels from './settings_panels';
 import initExperimentalFlags from './experimental_flags';
@@ -483,7 +484,7 @@ import OAuthRememberMe from './oauth_remember_me';
               new NotificationsDropdown();
               break;
             case 'wikis':
-              new gl.Wikis();
+              new Wikis();
               shortcut_handler = new ShortcutsWiki();
               new ZenMode();
               new gl.GLForm($('.wiki-form'), true);

app/assets/javascripts/main.js

@@ -161,7 +161,6 @@ import './username_validator';
 import './users_select';
 import './version_check_image';
 import './visibility_select';
-import './wikis';
 // eslint-disable-next-line global-require, import/no-commonjs
 if (process.env.NODE_ENV !== 'production') require('./test_utils/');

app/assets/javascripts/wikis.js

-/* eslint-disable no-param-reassign */
 /* global Breakpoints */
 import 'vendor/jquery.nicescroll';
 import './breakpoints';
-class Wikis {
+export default class Wikis {
   constructor() {
     this.bp = Breakpoints.get();
     this.sidebarEl = document.querySelector('.js-wiki-sidebar');
@@ -63,6 +62,3 @@ class Wikis {
     }
   }
 }
-
-window.gl = window.gl || {};
-window.gl.Wikis = Wikis;