This API is not used by any known themes/plugins, and is problematic for a few reasons
- It doesn't work on modern plugin connectors which have no wrapper element
- Making modifications to Ember-rendered DOM elements can lead to catastrophic and surprising errors
- It doesn't re-run when arguments to a plugin outlet change
This commit adds the deprecation notice, and refactors the tests so that they do not rely on any real core plugin outlets
b7cafdc07f