tcp: Remove unused tw_cookie_values from tcp_timewait_sock

tw_cookie_values is never used in the TCP-stack.

It was added by 435cf559 (TCPCT part 1d: define TCP cookie option,
extend existing struct's), but already at that time it was not used at
all, nor mentioned in the commit-message.

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>