Remove ValidationState's constructor

Summary:
Partial backport 2/3 of core PR17399:
https://github.com/bitcoin/bitcoin/pull/17399/commits/10e85d4adc9b7dbbda63e00195e0a962f51e4d2c

Depends on D8326.

Test Plan:

ninja all check

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8327