Change remaining GPLv2 headers to MIT

Change remaining GPLv2 headers to MIT

The files in question are copyright Benjamin Franzke (who agrees),
Intel Corporation, Red Hat and myself.  On behalf of Red Hat,
Richard Fontana says:

   "Therefore, to the extent that Red Hat, Inc. has any copyright
    interest in the files you cited as of this date (compositor-drm.c,
    compositor.c, compositor.h, screenshooter.c in
    http://cgit.freedesktop.org/wayland/wayland-demos/tree/compositor),
    Red Hat hereby elects to apply the CC0 1.0 Universal Public Domain
    Dedication to such copyrighted material.  See:
    http://creativecommons.org/publicdomain/zero/1.0/legalcode .

    Thanks,
    Richard E. Fontana
    Open Source Licensing and Patent Counsel
    Red Hat, Inc."