remove unnecessary 'js' subdir from services

part of the point of services is that they are just code, so they won't have js/less/etc. files.

IPython/html/static/notebook/js/notebook.js

@@ -8,7 +8,7 @@ define([
     'base/js/dialog',
     'notebook/js/textcell',
     'notebook/js/codecell',
-    'services/sessions/js/session',
+    'services/sessions/session',
     'notebook/js/celltoolbar',
     'components/marked/lib/marked',
     'highlight',

IPython/html/static/services/sessions/session.js

@@ -5,7 +5,7 @@ define([
     'base/js/namespace',
     'jquery',
     'base/js/utils',
-    'services/kernels/js/kernel',
+    'services/kernels/kernel',
 ], function(IPython, $, utils, kernel) {
     "use strict";