net: tcp_memcontrol: minor: remove unused variable

Commit 10b96f73 (``tcp_memcontrol: remove a redundant statement
in tcp_destroy_cgroup()'') says ``We read the value but make no use
of it.'', but forgot to remove the variable declaration as well. This
was a follow-up commit of 3f134619 (``memcg: decrement static keys
at real destroy time'') that removed the read of variable 'val'.

This fixes therefore:

  CC      net/ipv4/tcp_memcontrol.o
net/ipv4/tcp_memcontrol.c: In function ‘tcp_destroy_cgroup’:
net/ipv4/tcp_memcontrol.c:67:6: warning: unused variable ‘val’ [-Wunused-variable]
Signed-off-by: NDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_memcontrol.c

@@ -64,7 +64,6 @@ void tcp_destroy_cgroup(struct mem_cgroup *memcg)
 {
 	struct cg_proto *cg_proto;
 	struct tcp_memcontrol *tcp;
-	u64 val;
 
 	cg_proto = tcp_prot.proto_cgroup(memcg);
 	if (!cg_proto)