SharePoint 2016 on-premise

Is there a way to delete all workflows that show in the Workflow Inventory List for a site?

• The workflow inventory shows six workflows and all should be deleted because they are no longer necessary in the site. 
• Have many sites where the same workflows are published to when the site is created via workflow, but now need a method to delete those workflows when the sites are no longer active. It looks like the workflow that publishes the workflows from a library could be "reversed" to delete the workflows, using SOAP request. 
• Deleting the workflows from the hidden nintexworkflows library doesn't delete them from the Inventory List.