Clean out category and templating wikiisms

Rewrite links to the test cases for their actual location and remove links
to the now unusable templates. This allows the wiki category and templating
pages, which no longer function as expected as it's no longer a wiki.

The test case documentation is out-of-date, but rewriting this is out of
scope. See T6736.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>