Get "Create Revision" out of Quick Create menu for now

Summary:
Ref T12098.

We have two methods (supportsEditEngineConfiguration() and isEngineConfigurable()) which sort of do the same thing and probably should be merged.

For now, just swap which one we override to get "Create Revision" out of the Quick Create menu.

Test Plan: No more "Create Revision" in Quick Create menu.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12098

Differential Revision: https://secure.phabricator.com/D17204