Update wiki links in XSDs from index.php?title= to /wiki/

Description==

The wiki is now using short urls for article references. Example: https://wiki2.railml.org/wiki/IS:designator

The XSD still references old style urls like: https://wiki2.railml.org/index.php?title=IS:designator

Proposed solution

Replace "/index.php?title=" with "/wiki/" in all links to the railML wiki in the XSDs.