Remove findPruned and findFork, no more used after 17954.
Backport of Core [[https://github.com/bitcoin/bitcoin/pull/16426 | PR16426]] part [4/5] : https://github.com/bitcoin/bitcoin/pull/16426/commits/841178820d31e1c24a00cb2c8fc0b1fd2f126f56
Depends on D7936