[WPT maintenance] fixing xlink:href in tests

[karlcow]

In https://svgwg.org/svg2-draft/linking.html#XLinkRefAttrs

In previous versions of SVG, the ‘href’ attribute was specified in the XLink namespace [xlink] namespace. This usage is now deprecated and instead URL references should be specified using the ‘href’ attribute without a namespace.

Here is the list count of all occurences of xlink:href

list-xlink-href-deprecated.txt

There is probably an opportunity to modify some of the tests to href.

CLI to find the occurences in web-platform-tests/wpt/

grep -r "xlink:href" . --exclude-dir=.git | awk -F: '{print $1}' | sort | uniq -c | sort -rn | awk '{print $2 " | " $1}' > list-xlink-href-deprecated.txt