Drop ui-content class by default

Thx to Sven Franck

bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_html.xml

@@ -143,7 +143,7 @@
           data-gadget-scope="panel"\n
           data-gadget-sandbox="public"></div>\n
 \n
-  <article class="ui-content"></article>\n
+  <article></article>\n
 \n
   <section data-gadget-url="gadget_jio.html"\n
     data-gadget-scope="jio_gadget"\n