Function for deleting a key binding in a sparse keymap

[Lennart Borgman]

It would be good to have a function like this in Emacs:

(defun delete-key-in-sparse-map(sparse-map key)
 "In the sparse keymap SPARSE-MAP remove KEY.
In a sparse keymap if a key is bound to nil that means that
invoking that key find no binding in that map.  If instead there
is no binding at all then the default value if any in that keymap
is used.  This function removes any binding of KEY in the sparse
keymap SPARSE-MAP so that the default value will be used.

If SPARSE-MAP is not a sparse keymap an error is raised."

  ...
 )

However I do not know how to implement this for different formats for 
specifying the key.