Merge #12127: Remove unused mempool index
Summary:
PR12127 backport https://github.com/bitcoin/bitcoin/pull/12127/files
8e617e3 Remove unused mempool index (Suhas Daftuar)
Pull request description:
We haven't used the "mining_score" index since 0.12, so remove it.
Test Plan: make check
Reviewers: deadalnix, Fabien, jasonbcox, #bitcoin_abc
Reviewed By: deadalnix, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D3531