We have probably all done this.
When creating a workset for our Cad models if you forget to uncheck the box that says "visible by default in all views". Every time you create a view all the Cad files come in with it.
There is a fix.
Create a new workset making sure you uncheck the "visible by default in all views".
Then make the old workset editable by picking the button towards the bottom of the right of the window.
Then close the window and reopen it.
Highlight the old workset and pick the delete button on the right.
You will then be prompted where to move the information on the old workset.
Select the new workset.
The old workset disappears and you can then rename the new workset to whatever you like.
Thanks to Mike Jones for this tip.