Render public content as "Public" in headers, not "Public (No Login Required)"

Summary:
Ref T603. Although I think the parenthetical is valuable when //setting// policies to make sure no one accidentally opens content up, it's super annoying in headers.

This makes headers say "Public". Everything else still says "Public (No Login Required)".

Test Plan: {F69469}

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7310