Delete button should be hidden for last stage in pipeline

When viewing a pipeline that only has one stage, the delete button appears for that stage. When clicked, the following error appears. I assume this means that the last stage in a pipeline cannot be deleted. If that is the case, we should probably hide the delete button.

```
Could not update processing pipeline
Updating pipeline failed with status: There was an error fetching a resource: . Additional information: Not available
```