DEV: trash category definition topic instead of destroying. (PR #14356)

After deleting a category, we should soft-delete the category definition topic instead of hard deleting it. Else it causes issues while doing the user merge action if the source user has an orphan post that belongs to the deleted topic.

GitHub

Nice change.

We can remove the assertion above as it is testing the same thing.

I merged them into one line :slight_smile: