Consistently use phutil_console_confirm().

Summary:
PhutilConsole->confirm() is vestigial as noted in efcd70c, as
PhutilConsole may be deprecated sometime in the future. PhutilConsole
was developed as a tool for T4281 but the feature has been removed
since.

Replace existing occurences of the PhutilConsole->confirm() pattern with
phutil_console_confirm(). There should be no change in functionality
since the two functions are interchangeable.

Test Plan: Manually tested by running bin/arc lint, bin/arc diff --preview, bin/arc land --preview.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, alexmv

Differential Revision: https://secure.phabricator.com/D18185