Clean up mobile crumbs with multiple levels
Summary: Before the redesign, these levels were hidden. This recreates that behavior.
Test Plan:
Test nested Phriction pages
LICENSE1 KBDownload
README.md1 KBDownload
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D11621