migrate omniauth_callbacks:* to static bundle

app/assets/javascripts/dispatcher.js

@@ -277,11 +277,6 @@ var Dispatcher;
           break;
       }
       switch (path[0]) {
-        case 'omniauth_callbacks':
-          import('./pages/omniauth_callbacks')
-            .then(callDefault)
-            .catch(fail);
-          break;
         case 'admin':
           import('./pages/admin')
             .then(callDefault)

app/assets/javascripts/pages/omniauth_callbacks/index.js

 import initU2F from '../../shared/sessions/u2f';
 
-export default () => {
-  initU2F();
-};
+document.addEventListener('DOMContentLoaded', initU2F);