Don't prompt for patches when outputting lint results as XML.
Summary: The Checkstyle XML output format is not intended to be an interactive workflow.
Test Plan: Introduced linter issues and ran arc lint. Verified that no interactive prompt was shown.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9107