rxrpc: call->acks_hard_ack is now the same call->tx_bottom, so remove it

rxrpc: call->acks_hard_ack is now the same call->tx_bottom, so remove it

Now that packets are removed from the Tx queue in the rotation function
rather than being cleaned up later, call->acks_hard_ack now advances in
step with call->tx_bottom, so remove it.

Some of the places call->acks_hard_ack is used in the rxrpc tracepoints are
replaced by call->acks_first_seq instead as that's the peer's reported idea
of the hard-ACK point.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/20241204074710.990092-20-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>