validation: remove snapshot datadirs upon validation failure

Summary:

add utilities for deleting on-disk leveldb data

Used in later commits to remove leveldb directories for

• invalid snapshot chainstates, and
• background-vaildation chainstates that have finished serving their purpose.

https://github.com/bitcoin/bitcoin/pull/25667/commits/34d159033106cc595cfa852695610bfe419c989c

validation: remove snapshot datadirs upon validation failure

If a UTXO snapshot fails to validate, don't leave the resulting datadir
on disk as this will confuse initialization on next startup and we'll
get an assertion error.

https://github.com/bitcoin/bitcoin/pull/25667/commits/ad67ff377c2b271cb4683da2fb25fd295557f731

This is a partial backport of core#25667
Depends on D14653

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14654