Replace Differential "lint stars" with icons

Summary:
Ref T9764. These stars are inconsistent, not accessible, and generally weird. They predate icons.

Update them to use icons instead.

Test Plan:
{F8545721}

{F8545722}

{F8545723}

Maniphest Tasks: T9764

Differential Revision: https://secure.phabricator.com/D21640