OptionalObsoleteFiles.inc: Add rc.d/zfskeys

While here, sort the etc/rc.d entries.

PR: 256483
Reviewed by: allanjude
Approved by: allanjude (src)
MFC after: 3 days
Sponsored by: Modirum MDPay
Sponsored by: Klara Inc.
Differential Revision: https://reviews.freebsd.org/D33238