This allows us to reference assumeutxo configuration by blockhash as
well as height; this is helpful in future changes when we want to
reference assumeutxo configurations before the block index is loaded.
Also remove the unused assumeutxo checkpoint for block 210.
This is a partial backport of [[https://github.com/bitcoin/bitcoin/pull/27596 | core#27596]]
https://github.com/bitcoin/bitcoin/pull/27596/commits/b73d3bbd23220857bf17cbb6401275bf58013b72
Depends on D17633