Deprecate the "Commit is on autoclose/permanent branch" Herald "Commit" field

Summary:
Depends on D20426. Ref T13277. The new behavior is to fire Herald only once a commit becomes reachable from a permanent ref (previously, an "Autoclose" branch).

That means that every "Commit" Herald rule implicitly has this field as a condition, and it no longer does anything.

Test Plan: Wrote a Herald rule, saw this as an option in the "Deprecated" section.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13277

Differential Revision: https://secure.phabricator.com/D20427