Summary: Removes AphrontPanelView, and most of it's CSS - it seems some old previews still call it.
Test Plan: grep for AphrontPanelView, no callsites left. Verify CSS left is minimal needed.
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T7427
Differential Revision: https://secure.phabricator.com/D12004
8da5b6255d