Currently you can not delete them. We wanted to get feedback on whether or not that is needed or if you can just ignore an unused playbook for now. It is much more efficient for us to reuse playbooks than to delete them and then possibly create new ones. We will be adding in the feature to load an existing playbook in to another one, so hopefully that will alleviate some of the desire to delete them. If we can get by without the delete option, I would prefer that.