selftests: tcp: Remove broken SNMP assumptions for TCP AO self-connect tests.

tcp_ao/self-connect.c checked the following SNMP stats before/after
connect() to confirm that the test exercises the simultaneous connect()
path.

  * TCPChallengeACK
  * TCPSYNChallenge

But the stats should not be counted for self-connect in the first place,
and the assumption is no longer true.

Let's remove the check.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Dmitry Safonov <dima@arista.com>
Link: https://patch.msgid.link/20240710171246.87533-3-kuniyu@amazon.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>