Fix flush object boxes on mobile

Summary: On /differential/ we have flush lists inside an object box which on mobile had unwanted padding. This padding shouldn't be set anymore.

Test Plan: Reviewed mobile home, differential, maniphest, applications, and uiexamples, noticed no artifacts to removal.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11858