Remove the test EnhancedEntityBundle, it is not needed

Our tests are not really using EnhancedEntityBundle, we just have boilerplate where we need to create a bundle in every test.

The main reason why I want to remove it is because I want to add more entity types (such as EnhancedEntityWithOwner), and it would be annoying to have to keep defining bundle entities for consistency reasons.

Of course, we'll define a few test bundles in a hook.

This will require converting BundleEntityAccessControlHandlerTest from a kernel test to a unit test, but that will also increase the coverage of its permissions.