docs/ci: remove default nginx config, which we don't need for proxy

Signed-off-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24445>

docs/ci/bare-metal.rst

@@ -215,6 +215,7 @@ Enable the site and restart nginx:
 
 .. code-block:: console
 
+   sudo rm /etc/nginx/sites-enabled/default
    sudo ln -s /etc/nginx/sites-available/fdo-cache /etc/nginx/sites-enabled/fdo-cache
    sudo systemctl restart nginx