migrate projects:branches:index to static bundle

app/assets/javascripts/dispatcher.js

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

app/assets/javascripts/pages/projects/branches/index/index.js

 import AjaxLoadingSpinner from '~/ajax_loading_spinner';
 import DeleteModal from '~/branches/branches_delete_modal';
 
-export default () => {
+document.addEventListener('DOMContentLoaded', () => {
   AjaxLoadingSpinner.init();
   new DeleteModal(); // eslint-disable-line no-new
-};
+});