Remove "commit hook mode" check from Javelin linter
Summary: Ref T7674. Commit hook mode is going away.
Test Plan: Eyeball it.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T7674
Differential Revision: https://secure.phabricator.com/D12712