[refactor] rename variables in AcceptPackage for clarity

Summary:
Partial backport of core#26646:
https://github.com/bitcoin/bitcoin/pull/26646/commits/dae81e01e8698e04afb0db4d1442659c3b48fcf5

Depends on D16401.

Test Plan:

ninja all check

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16402