Remove placeholder

Summary: See discussion in D3103. We don't need this for now; if we do in the future we should probably use an alternate implementation.

Test Plan: Grepped for 'placeholder', viewed UI examples.

Reviewers: vrana

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1569

Differential Revision: https://secure.phabricator.com/D3115