Remove 'setShadow' from PHUIBoxView
Summary: Removes setShadow, uses setBorder instead
Test Plan: Tested multicolumn, feed, search box, many other areas. Things look less 3d.
Reviewers: epriestley, btrahan
Reviewed By: epriestley
CC: Korvin, epriestley, aran
Differential Revision: https://secure.phabricator.com/D8192