remove js styling, already done in css in logoutmain

IPython/html/static/auth/js/logoutmain.js

@@ -4,7 +4,6
 var ipython = ipython || {};
 require(['base/js/page'], function(page) {
     var page_instance = new page.Page();
-    $('#ipython-main-app').addClass('border-box-sizing');
     page_instance.show();
 
     ipython.page = page_instance;