migrate projects:compare:show to static bundle

app/assets/javascripts/dispatcher.js

@@ -48,11 +48,6 @@ var Dispatcher;
         case 'projects:issues:show':
           shortcut_handler = true;
           break;
-        case 'projects:compare:show':
-          import('./pages/projects/compare/show')
-            .then(callDefault)
-            .catch(fail);
-          break;
         case 'projects:branches:new':
           import('./pages/projects/branches/new')
             .then(callDefault)

app/assets/javascripts/pages/projects/compare/show/index.js

 import Diff from '~/diff';
 import initChangesDropdown from '~/init_changes_dropdown';
 
-export default () => {
+document.addEventListener('DOMContentLoaded', () => {
   new Diff(); // eslint-disable-line no-new
   const paddingTop = 16;
   initChangesDropdown(document.querySelector('.navbar-gitlab').offsetHeight - paddingTop);
-};
+});