Inline Sign1 and SignN
Summary:
Sign1 and SignN are kind of redundant so remove them and inline their
behavior into SignStep
This is a partial backport of Core PR13425 : https://github.com/bitcoin/bitcoin/pull/13425/commits/b6edb4f5e6e0bf0f9c7dd26a125849f0103b44cd
Test Plan:
make check
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D4209