Remove config argument from blockToJSON

Summary:
Was added in "move-only" diff D717.
It is not used anymore since introduction of TxToUniv in D2499.

Depends on D3014

Test Plan: make check

Reviewers: #bitcoin_abc, deadalnix, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3070