Lint JSON files with ArcanistJSONLinter.

Summary: After D9628, we can lint JSON files natively.

Test Plan: Linted a few JSON files manually (i.e. arc lint --trace -- $FILE).

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9652