kern_rangelock.c: add Foundation copyright, remove sys/cdefs.h include
Also drop 'All rights reserved' line from my copyright.
Reviewed by: markj, Olivier Certner <olce.freebsd@certner.fr>
Discussed with: emaste (whole series)
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D41787