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