tcp: Remove timewait_sock_ops.twsk_destructor().

tcp: Remove timewait_sock_ops.twsk_destructor().

Since DCCP has been removed, sk->sk_prot->twsk_prot->twsk_destructor
is always tcp_twsk_destructor().

Let's call tcp_twsk_destructor() directly in inet_twsk_free() and
remove ->twsk_destructor().

While at it, tcp_twsk_destructor() is un-exported.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250822190803.540788-3-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>