Remove spacer from sidebars.

Summary: This removes all calls to addSpacer and the method. We were applying it inconsistently and it was causing spacing issues with redesigning the sidenav. My feeling is we can recreate the space in CSS if the design dictates, which would apply it consistently.

Test Plan: Go to Applications, click on every application.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4420