MAINTAINERS: remove myself as a Reviewer for Ceph

It has been a couple of years since I stepped down as CephFS maintainer.
I'm not involved in any meaningful way with the project these days, so
while I'm happy to help review the occasional patch, I don't need to be
cc'ed on all of them.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>