Mark diviner atoms as closed in search index

Summary: Ref T4558. If a Diviner atom is a ghost (i.e. the underlying source code has been removed), mark it as closed in the search index.

Test Plan: Searched for a ghost atom in global searcn and saw the results show "Closed".

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T4558

Differential Revision: https://secure.phabricator.com/D13297