R1:d2ead465f38e

Remove "Close Task" button

Summary: Fixes T5134

Test Plan: Went to a task, closed it. Felt satisfied.

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley, Korvin

Maniphest Tasks: T4657, T5134

Differential Revision: https://secure.phabricator.com/D9221