security: remove unused forwards

Why would linux/security.h need forward declarations for nfsctl_arg and
swap_info_struct?  It's hard to imagine: remove them.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>