netlink: remove unnecessary forward declaration

netlink_skb_destructor() is actually defined before the first usage
in the file, so remove the unnecessary forward declaration.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -128,7 +128,6 @@ static const char *const nlk_cb_mutex_key_strings[MAX_LINKS + 1] = {
 };
 
 static int netlink_dump(struct sock *sk);
-static void netlink_skb_destructor(struct sk_buff *skb);
 
 /* nl_table locking explained:
  * Lookup and traversal are protected with an RCU read-side lock. Insertion