fixup! web_renderjs_ui: py3

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSection_renderDefaultPageAsGadget.py

 import json
 import re
-from six.moves.urllib.parse import urljoin
 from Products.ERP5Type.Utils import bytes2str, str2bytes
 
 if REQUEST is None:
@@ -41,6 +40,12 @@ if selected_language == default_language:
 else:
   base_prefix = '../'
 
+def urljoin(base, url):
+  # concemtually similar to urllib.parse.urljoin, but without trying to eliminate
+  # .. path elements, because we want to produce relative URLs that may be parent
+  # of the base.
+  return base_prefix + url
+
 mapping_dict = {
   "base_prefix": base_prefix,
   "frontpage_gadget": web_section.getLayoutProperty("configuration_frontpage_gadget_url", default="worklist"),