tests/qapi-schema: Bury dead test case doc-non-first-section

tests/qapi-schema: Bury dead test case doc-non-first-section

The test passed when it was added.  However, the commit adding it
neglected to make Meson aware of it, so it never ran automatically.
The test stopped making sense when we changed headings markup, and
ceased to pass then.  It should've been removed then.  Do that now.

Fixes: 6c10778826a8 (docs/sphinx: remove special parsing for freeform sections)
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20250724091742.1950167-3-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>