releasing: Use the release script from wayland

The release script from the Wayland repository is simpler than the
script from Xorg, uses the releases from gitlab and is now generic
enough to be used by different projects.

Update the release procedure to use that script instead.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Simon Ser <contact@emersion.fr>