lsm: remove old email address for Stephen Smalley

Remove my old, no longer functioning, email address from comments.
Could alternatively replace with my current email but seems
redundant with MAINTAINERS and prone to being out of date.

Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
[PM: subject tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>