xfrm: remove unneeded method typedef declaration in net/xfrm.h.

The patch removes unneeded method typedef declaration (icv_update_fn_t
) and the two struct declarations which appear in its prototype
(struct hash_desc and struct scatterlist) in net/xfrm.h.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>