[validation] remove PackageMempoolAcceptResult::m_package_feerate
Summary:
This value creates an extremely confusing interface as its existence is dependent upon implementation details (whether something was submitted on its own, etc). MempoolAcceptResult::m_effective_feerate is much more helpful, as it always exists for submitted transactions.
Partial backport of core#26646:
https://github.com/bitcoin/bitcoin/pull/26646/commits/5eab397b9840de5a4729bea723794b529e5fcbb4
Depends on D16399.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D16400