[FIX] correction of the link given to google to access the sitemap

by using the file tiki-sitemap.php we generate one more time an existing file the worry is that it brings back a bug to google because apart from the xml file which contains the pages, it does not manage to recover the others. however by giving simpleent the natural access path all happens without worries. https://avan.tech/item71198 https://avan.tech/item67343