security: remove dead hook sb_post_addmount

Unused hook.  Remove.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

diff --cc fs/namespace.c
Simple merge

diff --cc include/linux/security.h
Simple merge

diff --cc security/capability.c
Simple merge

diff --cc security/security.c
Simple merge