Declare unused function ediff-user-grabbed-mouse obsolete

Declare unused function ediff-user-grabbed-mouse obsolete

* lisp/vc/ediff-init.el (ediff-user-grabbed-mouse): Declare unused
function obsolete.  As far as I can tell, this has been unused
since 1996.

* lisp/vc/ediff-wind.el (ediff-mouse-pixel-position): Make
variable obsolete.  It is only used in the above obsolete funct
* lisp/vc/ediff-mult.el (ediff-filegroup-action)
(ediff-registry-action):
* lisp/vc/ediff-util.el (ediff-setup): Don't set above unused
variable.

* lisp/vc/ediff-init.el (ediff-spy-after-mouse): Make obsolete.
* lisp/vc/ediff-util.el (ediff-setup): Don't add above obsolete
function to pre-command-hook.