git_sha1_gen.py: fix out-of-date comment

This hasn't been true since 7088622e5fb506b64c90 ("buildsys: move file
regeneration logic to the script itself") almost 3 years ago.

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5112>
1 file changed