Remove "Flags" from homepage

Summary: Flags have a large red count on the homepage now, which I think is a sufficient reminder of flagged stuff. This element was nice at first to raise awareness of the app, but it's fairly well integrated now and enjoys moderate use. This is also a sort of feeler for how much people use it / the homepage in general.

Test Plan: Looked at homepage, no flags.

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D4479