cursor: Remove "weston" from anonymous shm filenames

This mildly confused me during some debugging, so I guess it wouldn't
hurt to make the filename more indicative of where it was actually
created.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Giulio Camuffo <giuliocamuffo@gmail.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>