R1:fc1c633bae85

fix Vary Subjects option names

Summary:
The option names for `Vary Subjects` are copypasta from the `Add "Re:" Prefix` option. Fix their names to refer to `Vary Subjects` instead.

Fixes T11148

Test Plan: Verify option names for `Vary Subjects` refer to `Add "Re:" Prefix` before apply. Verify they no longer do after apply.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T11148

Differential Revision: https://secure.phabricator.