netfilter: conntrack: Remove unused variable declaration

commit e97c3e27 ("tproxy: split off ipv6 defragmentation to a separate
module") left behind this.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/ipv6/nf_conntrack_ipv6.h

@@ -4,7 +4,4 @@
 
 extern const struct nf_conntrack_l4proto nf_conntrack_l4proto_icmpv6;
 
-#include <linux/sysctl.h>
-extern struct ctl_table nf_ct_ipv6_sysctl_table[];
-
 #endif /* _NF_CONNTRACK_IPV6_H*/