tcp: remove RFC3517/RFC6675 tcp_clear_retrans_hints_partial()

Now that we have removed the RFC3517/RFC6675 hints,
tcp_clear_retrans_hints_partial() is empty, and can be removed.

Suggested-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250615001435.2390793-4-ncardwell.sw@gmail.com


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