migrate dashboard:merge_requests to static bundle

app/assets/javascripts/dispatcher.js

@@ -53,11 +53,6 @@ var Dispatcher;
         case 'projects:issues:show':
           shortcut_handler = true;
           break;
-        case 'dashboard:merge_requests':
-          import('./pages/dashboard/merge_requests')
-            .then(callDefault)
-            .catch(fail);
-          break;
         case 'groups:issues':
           import('./pages/groups/issues')
             .then(callDefault)

app/assets/javascripts/pages/dashboard/merge_requests/index.js

 import projectSelect from '~/project_select';
 import initLegacyFilters from '~/init_legacy_filters';
 
-export default () => {
+document.addEventListener('DOMContentLoaded', () => {
   projectSelect();
   initLegacyFilters();
-};
+});