These manual calls to Unload() are no longer necessary because
CBlockIndex's no longer live in the heap as of the previous commit.
This is a partial backport of [[https://github.com/bitcoin/bitcoin/pull/24050 | core#24050]]
https://github.com/bitcoin/bitcoin/pull/24050/commits/531dce034718523967808a89c18ba69a1e3e5a1f
Depends on D12991