refactor: Remove unused request.fHelp
Summary:
This concludes backport of core#19250 [2/2]
https://github.com/bitcoin/bitcoin/pull/19250/commits/fadf6bd04f002d05aaff8eba74015e25a41966bc
Depends on D9455
Test Plan: ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D9456