By design there are some nodes that cannot be deleted from the app workflow. When using an app template such as Generic Input Adapter and Propensity Scoring there is an expected minimum workflow to make the app properly functional. Any nodes on this default workflow that are inserted onto the canvas immediately after initial creation cannot be removed. Process nodes along with child output nodes added to the workflow by the user can typically be removed.
At this point in time, output nodes cannot be removed without removing the parent process node, and parent process nodes cannot be removed without removing child output nodes.