Allow diviner books to be permanently destroyed

Summary: Fixes T7182.

Test Plan: Deleted a book with ./bin/remove destroy

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7182

Differential Revision: https://secure.phabricator.com/D11742