doc: gitk: remove gitview reference

contrib/gitview has been removed. Remove the reference.

Signed-off-by: Philip Oakley <philipoakley@iee.org>
Reviewed-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitk.txt

@@ -187,10 +187,6 @@ SEE ALSO
 'qgit(1)'::
 	A repository browser written in C++ using Qt.
 
-'gitview(1)'::
-	A repository browser written in Python using Gtk. It's based on
-	'bzrk(1)' and distributed in the contrib area of the Git repository.
-
 'tig(1)'::
 	A minimal repository browser and Git tool output highlighter written
 	in C using Ncurses.