[backport#12727] Remove unreachable help conditions

Summary:
https://github.com/bitcoin/bitcoin/pull/12727/commits/e5468a19d14a32715097435df778d43efcceaa11

Depends on D6593

Backport of Core PR12727

Test Plan:

ninja

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6594