tcp: Remove unused tcpct declarations and comments

Remove declaration, 4 defines and confusing comment that are no longer used
since 1a2c6181c4 ("tcp: Remove TCPCT").

Signed-off-by: Dmitry Popov <dp@highloadlab.com>
Acked-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/linux/tcp.h
Simple merge

diff --cc include/net/tcp.h
Simple merge

diff --cc net/ipv4/tcp.c
Simple merge