Remove 1x AppIcons, use FontIcons instead

Summary: Removes the 1x application icons, and uses the fonticons instead. Feed was only known location.

Test Plan:
feed, dashboards, grep for use

{F275636}

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: hach-que, Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11496