Permanently remove license linters

Summary: For eventual commit.

Test Plan: none

Reviewers: nh, btrahan

Reviewed By: btrahan

CC: aran, vrana, FacebookPOC

Maniphest Tasks: T2274

Differential Revision: https://secure.phabricator.com/D4907
Merge branch 'master' of http://github.com/facebook/arcanist