Remove unused legacy CHashVerifier
Summary:
This concludes backport of core#25284
https://github.com/bitcoin/bitcoin/pull/25284/commits/fa626af3edbe8d98b2de91dd71729ceef90389fb
Depends on D19057
Test Plan: ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D19142