remove redundant 'responsive-utilities' from style.less

it's already included in bootstrap.less

IPython/html/static/style/style.less

@@ -1,30 +1,29 b''
 /*!
 *
 * Twitter Bootstrap
 *
 */
 @import "../components/bootstrap/less/bootstrap.less";
-@import "../components/bootstrap/less/responsive-utilities.less";
 
 /*!
 *
 * Font Awesome
 *
 */
 @import "../components/font-awesome/less/font-awesome.less";
 @fa-font-path:    "../components/font-awesome/fonts";
 
 // base
 @import "../base/less/style.less";
 @import "../base/less/page.less";
 
 // auth
 @import "../auth/less/style.less";
 
 // tree
 @import "../tree/less/style.less";
 
 // notebook
 @import "../notebook/less/style.less";