xcursor: Change keithp licensed code from X11 to Expat license

The license text for this file mentions Keith Packard specifically,
however it is otherwise identical to all the other MIT X11 licensed code
in Wayland, and so can be changed to the substantially identical MIT
Expat license.

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