R1:ea7397f7e4f9

Rename PassphraseCredentialType subclasses for consistency

Summary: Ref T5655.

Test Plan: `arc unit` + `grep`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D13266