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