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The test case documentation is out-of-date, but rewriting this is out of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>

The release documentation currently live under `content/<version>/`, move
it into it's own section. This cleans up the content directory and may
enable us to do fancy things with Hugo templating further down the line.

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