netfilter: remove unused #include <version.h>

The file(s) below do not use LINUX_VERSION_CODE nor KERNEL_VERSION.
  net/netfilter/nf_tproxy_core.c

This patch removes the said #include <version.h>.

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>