Remove "Editable By" description fields in Passphrase, Phame, and Spaces

Summary:
Ref T13411. These three applications render an "Editable By: <policy>" field in their descriptions.

The pages that these appear on all have "Edit <thing>" actions which either tell you the policy or allow you to discover the policy, and this field is unusual (the vast majority of objects don't have it). I think it largely got copy/pasted or used as space-filler and doesn't offer much of value.

Remove it to simplify/standardize these pages and make changes to how this field works simpler to implement.

Test Plan: Viewed a Credential, Blog, and Space; no longer saw the "Editable By" field.

Maniphest Tasks: T13411

Differential Revision: https://secure.phabricator.com/D20802