net: Remove leftover include from nftables.h

Commit db3685b4 ("net: remove obsolete members from struct net")
removed the uses of struct list_head from this header, without removing
the corresponding included header.
Signed-off-by: Jörn-Thorben Hinz <jthinz@mailbox.tu-berlin.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netns/nftables.h

@@ -2,8 +2,6 @@
 #ifndef _NETNS_NFTABLES_H_
 #define _NETNS_NFTABLES_H_
 
-#include <linux/list.h>
-
 struct netns_nftables {
 	u8			gencursor;
 };