Strangly I seem not to be able to delete an existing workflow as a whole, nor a state within a workflow. The admin user has all the necessary permission. No content type is assigned with the workflow. What do I not see?
In Drupal 8 (at least), there is a "Clean up" tab in the main configuration screen of the module (/admin/config/workflow/workflow), where you can delete inactive states.
In my case, I suddenly stopped seeing the "Actions" buttons, so the only thing I could do was activate/disactivate the states.
That may solve someone's problem...It solved mine
I was just having the same issue. But I have just noticed that deleting a state from a workflow is not done in just one step.
First, you have to disable the state.
Second, on the main page of the workflow module, click on "Clean up workflow" and you will see that you can delete the inactive workflows there.
If you want to delete a workflow at all it must not be used in any node. So delete all fields pointing to this workflow first.
But I confirm: I cannot delete single states inside of a workflow at all.