Minor cleanup of linter testing code.

Summary:
Just some minor cleaning up, including:

- Removing old annotations for Diviner.
- Renaming some `lint-test` files so that the directory name bears a closer resemblance to that of the linter.
- Remove some useless `return` statements.

Test Plan: `arc unit`.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9096