Here's what I ended up doing to get rid of an old/duplicate wishlist, it took Amazon about a day to complete the deletion.
1. I initiated a chat session with Amazon support, they told me that they would need the following info (either submitted in to the website or emailed to them) to delete the old wishlist.
- E-mail address used while creating Wish List.
- Shipping address associated with Wish List.
- First three items on the Wish List.
- URL of the Wish List page, if possible.
3. Since I couldn't login with that old email address, I went thru the Amazon Contact Us page again and instead of the Chat I picked Email and provided the requested info.
24 hours later the old wish list was gone.
This answer is buried in a support post on an Amazon Discussions page.