Convert more linters to modern formats with `.arclint` support

Summary:
Ref T3186. Ref T2039.

  - Convert JSHint to modern format; improve granularity of errors.
  - Convert PyFlakes to modern format;
  - Remove ApacheLicenseLinter and LicenseLinter (these have been deprecated for a very long time).

This is somewhat disruptive and will break some users by no longer respecting various path/config options. I'll sequence documentation and deprecation warnings in front of these.

Test Plan: Ran unit tests.

Reviewers: btrahan, #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin, joshuaspence, aran

Maniphest Tasks: T3186, T2039

Differential Revision: https://secure.phabricator.com/D6810