Rename `PhabricatorDestructableInterface` interface

Summary: Ref T5655. The `PhabricatorDestructibleInterface` interface is misspelled as `PhabricatorDestructableInterface`. Fix the spelling mistake.

Test Plan: `grep`. Seeing as this interface is fairly recent, I don't expect that this would cause any widespread breakages.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D9988