[9.x] Remove assertDeleted

[jasonmccreary]

This removes the asymmetrical, proxy assertion assertDeleted. Unlike other assertions, its opposite assertion does not exist (assertNotDeleted). It is also superseded in #38766 by assertModelExists and assertModelMissing.

Tests using this assertion may either adopt one of these more communicative methods, or fallback to the original assertDatabaseMissing.

Targeting Laravel 9 as this is a breaking change. Alternatively, I am glad to open a PR to add assertNotDeleted to provide symmetry. I believe removal is cleaner though as all paths should be covered by the other 4 assertions.

[taylorotwell]

What are the current differences between assertDeleted and assertModelMissing?

[jasonmccreary]

@taylorotwell, when passed a model, none. They both call assertDatabaseMissing underneath (ref, ref)

I originally added assertDeleted (#30648). I'm not sure why I made it a proxy method and didn't add its counterpart. 😅 🤦

As you can see from my original example, it was intended to do what assertModelExists and assertModelMissing ultimately did.