Workflow is a technology preview feature and is disabled by default.
A workflow can only be deleted by the owner of the workflow, or a user with super user rights.
To delete a workflow:
If projects, or branches are associated with the workflow, the Delete button is muted, and the workflow cannot be deleted.
For instructions on how to remove the workflow from a project, or branch, see Associate a workflow with the project and Associate a workflow with the project branch.