MAINTAINERS: Remove myself as LED subsystem maintainer

It don't have enough time for reviewing patches and thus don't
want to be listed as regular LED maintainer. Nonetheless I may still
give a review from time to time.

Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>