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

{F281114}

{F281115}

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11621