cursor: Update printed license from MIT "X11" to MIT "Expat"

The code generates a cursor-data.h file, with licensing information.
Change this from the MIT "X11" license to MIT "Expat" license for
consistency with the rest of Wayland.

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>