fixup! erp5_interface_post: factorizes code used to generate a Post from an Event

bt5/erp5_interface_post/SkinTemplateItem/portal_skins/erp5_interface_post/Event_createPostMessage.py

@@ -13,7 +13,6 @@ post_message_post_module = portal.getDefaultModuleValue(post_portal_type, None)
 message_post = post_message_post_module.newContent(
   portal_type=post_portal_type,
   title="Post Message for %s" % context.getTitle(),
-  reference=context.getReference(),
   data=post_message_data,
 )
 message_post.edit(**kw)