How do I delete a rubric?
Go to the Rubrics tool.

Select the Rubrics tool from the Tool Menu of your site.
Select the X icon for the rubric you would like to delete.
Note: Locked rubrics, denoted by a Lock icon next to the rubric’s title, cannot be deleted. If you need to delete a locked rubric, you must first detach it from the activity or activities in your course site where it is being used.