Revert "Load jQuery instead of jQueryUI only when require('jquery-ui') === undef"

This reverts commit 5a77151.

Author: inside-hakumai

src/jupyter_nbextensions_configurator/static/nbextensions_configurator/tree_tab/main.js

@@ -1,11 +1,7 @@
 define(function (require, exports, module) {
     "use strict";
 
-    var $ = require('jquery-ui');
-    if ($ === undefined) {
-        $ = require('jquery');
-    }
-
+    var $ = require('jquery');
     var nbextensions_configurator = require('../main');
     var rendermd = require('../render/render');