bug#65245: Possible code removal in eshell/diff (em-unix.el)

[Richard Hopkins <emacs@unbit.co.uk>]

Hi,
I think the use of `compilation-finish-functions' and
#'current-window-configuration can be removed from #'eshell/diff
as it's no longer called and the intended functionality is achieved
elsewhere.

For example the below works with/without the 
`compilation-finish-functions'.

   $ emacs -Q -f eshell
   # in the eshell buffer
   echo a > a
   echo b > b
   diff -u a b
   # pops a #'diff-mode window with font-lock enabled; press q to quit

Here are some commits showing the introduction and then others
that help make it no longer relevant.

2001-04-24 ef59cfc6638a8ac3fccbee88482d142e95c32f81
	   Use `compilation-finish-functions' in #'eshell/diff

2004-02-02 c010ecfa9a26549486bb00c39221813c02c615de
            Bind q to #'quit-window in `diff-mode-shared-map'

2004-02-11 540d066630c55ab957dc08aa7abbca7775c9bd7b
	   #'diff - don't use compile any more, use diff-mode instead.

2011-02-01 abef340a0c5304054a2a5e6d95e1d825501f0e7a
	   `diff-mode-shared-map' inherit from `special-mode-map'

Best,
Richard