During my progress on updating cc_cubic to RFC9438, found such redundancy as:
(1) W_est: we use the alternative stack local variable `W_est` in
cubic_ack_received()
(2) cwnd_prior: it is used for Reno-Friendly Region in RFC9438 Section 4.3,
but we use the alternative cwnd from NewReno for Reno-Friendly
as in commit ee45061051715be4704ba22d2fcd1c373e29079d
- W_est: we use the alternative stack local variable `W_est` in `cubic_ack_received()`.
- cwnd_prior: it is used for Reno-Friendly Region in RFC9438 Section 4.3, but we use the alternative cwnd from NewReno for Reno-Friendly as in commit ee45061051715be4704ba22d2fcd1c373e29079d.
No functional change intended.