mempool: Removed the ancestor_score index
Summary:
This is no longer being used (it was used previously for mining). After the CPFP-removal from the mining code in a previous commit, this index is no longer needed. Also removed the comparator CompareTxMemPoolEntryByAncestorFee and the tests for this index and comparator.
Port of bchn#1113.
Depends on D13122.
Test Plan:
ninja all check
Reviewers: #bitcoin_abc, PiRK, sdulfari
Reviewed By: #bitcoin_abc, PiRK, sdulfari
Differential Revision: https://reviews.bitcoinabc.org/D13123