[IPSEC]: Kill duplicate xfrm_policy_flush prototype

For five years we had two xfrm_policy_flush prototypes and every time that
function's signature changed people have been diligently updating both of
them without noticing :)
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/xfrm.h

@@ -1310,7 +1310,6 @@ extern int xfrm_alloc_spi(struct xfrm_state *x, u32 minspi, u32 maxspi);
 struct xfrm_state * xfrm_find_acq(u8 mode, u32 reqid, u8 proto,
 				  xfrm_address_t *daddr, xfrm_address_t *saddr,
 				  int create, unsigned short family);
-extern int xfrm_policy_flush(u8 type, struct xfrm_audit *audit_info);
 extern int xfrm_sk_policy_insert(struct sock *sk, int dir, struct xfrm_policy *pol);
 extern int xfrm_bundle_ok(struct xfrm_policy *pol, struct xfrm_dst *xdst,
 			  struct flowi *fl, int family, int strict);