Remove duplicate "Change Default Values" action in form editing workflow

Summary: Fixes T12434. I accidentally copy/pasted this too much in D17442.

Test Plan: Viewed a form edit page, no longer saw two copies of this action.

Reviewers: chad, cspeckmim

Reviewed By: chad, cspeckmim

Maniphest Tasks: T12434

Differential Revision: https://secure.phabricator.com/D17530