Deleting an issue type does not make workflows become inactive

Steps to reproduce:

• Create a workflow called "Foo Workflow"
• Confirm that the workflow is inactive
• Create an issue type called "Stuff"
• Edit an existing active workflow scheme
  Associate the Foo Workflow with the Stuff Issue type.
• Confirm that the workflow is now active
• Delete the Issue Type

Expected:
The Foo Workflow is inactive again

Actual:
The Foo Workflow is listed as active but associated with no schemes