Remove leftover code for "postponed" lint and unit status

Summary: Ref T9134. It looks like this functionality was removed in D13848.

Test Plan: Submitted a diff successfully.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T9134

Differential Revision: https://secure.phabricator.com/D13869