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