Delete friend button is working! Instructions here:

Just like the buttons for Add Friend, Confirm Request, and Deny Request,
this button can be added to any page and will work with no additional
coding from you. 

You still need to style the button using CSS, but you can import
userThumbnail.css to use my styling.

To delete your friend with userid=3, add the following:
<input onclick="deleteFriend(this)" value="Delete Friend"
id="deleteFriendButtonId-3" />

Your restrictions are that you must reference the correct callback
function for onclick, and you must have the ID formatted as
deleteFriendButtonId-X, where X is the friend's ID.