...since the height information in already in CBlockIndex* and we can
use an easy custom sorter.
This is a partial backport of core#24515
https://github.com/bitcoin/bitcoin/pull/24515/commits/42e56d9b188f97c077ed2269e24acc0be35ece17
Also includes a comment removal from https://github.com/bitcoin/bitcoin/pull/24515/commits/3bbb6fea051f4e19bd2448e401a6c4e9b4cc7a41
The rest of this commit is already done in Bitcoin ABC (review of D12993 and D12994)
Depends on D13020