Hide footer on mobile Conpherence

Summary: This has been causing scrolling issues for me for a while, turns out the footer behind the Conpherence layout can bubble up and cause scrolling issues if you don't hit the scrollarea in the right place with your finger. Hiding it via CSS or removing the footer in the configuration resolves the issue on my phone on secure.

Test Plan: Test with and without footer on secure, hide footer in CSS since it's not visible anyways.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16732