migrate sessions:new to static bundle

app/assets/javascripts/dispatcher.js

@@ -49,11 +49,6 @@ import SearchAutocomplete from './search_autocomplete';
       });
 
       switch (page) {
-        case 'sessions:new':
-          import('./pages/sessions/new')
-            .then(callDefault)
-            .catch(fail);
-          break;
         case 'projects:boards:show':
         case 'projects:boards:index':
           import('./pages/projects/boards')

app/assets/javascripts/pages/sessions/new/index.js

@@ -2,10 +2,10 @@ import UsernameValidator from './username_validator';
 import SigninTabsMemoizer from './signin_tabs_memoizer';
 import OAuthRememberMe from './oauth_remember_me';
 
-export default () => {
+document.addEventListener('DOMContentLoaded', () => {
   new UsernameValidator(); // eslint-disable-line no-new
   new SigninTabsMemoizer(); // eslint-disable-line no-new
   new OAuthRememberMe({ // eslint-disable-line no-new
     container: $('.omniauth-container'),
   }).bindEvents();
-};
+});