net: skbuff: drop the linux/splice.h include

splice.h is included since commit a60e3cc7 ("net: make
skb_splice_bits more configureable") but really even then
all we needed is some forward declarations. Most of that
code is now gone, and remaining has fwd declarations.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -29,7 +29,6 @@
 #include <linux/dma-mapping.h>
 #include <linux/netdev_features.h>
 #include <net/flow_dissector.h>
-#include <linux/splice.h>
 #include <linux/in6.h>
 #include <linux/if_packet.h>
 #include <linux/llist.h>