tcp: Remove unused function declarations

commit 8a59f9d1 ("sock: Introduce sk->sk_prot->psock_update_sk_prot()")
left behind tcp_bpf_get_proto() declaration. And tcp_v4_tw_remember_stamp()
function is remove in ccb7c410 ("timewait_sock: Create and use getpeer op.").
Since commit 68698970

 ("tcp: simplify tcp_mark_skb_lost")
tcp_skb_mark_lost_uncond_verify() declaration is not used anymore.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230729122644.10648-1-yuehaibing@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>