Avoid double [y/N] when updating a not owned revision

Summary:
Since 737f5c0df976fe2b3178aac6ab7feb3d3621d99e arcanist shows [y/N] two times, when arcanist asks you, if you want to proceed, if you want to update a not owned revision. Ths patch fixes
that, so that Arcanist shows [y/N] only once, like at other situations, when Arcanist asks you a question.
Ref T11489

Test Plan: Updated a not owned revision.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley

Tags: Arcanist

Maniphest Tasks: T11489

Differential Revision: https://secure.phabricator.com/D16415