Remove the NEWS writeup mention of gist

Chris and I both tried, but something about our bext opencv build is
giving us linking errors on Windows so we can't roll binaries with it
included.  Leaving the NEWS line, as it is available to build if a
system OpenCV is available.

NEWS

@@ -23,10 +23,6 @@ processing high level assemblies in BRL-CAD's example geometry files:
 % success, old: 88.9%  (249 of 280) Time elapsed:  7256 seconds
 % success, new: 98.9%  (277 of 280) Time elapsed:  1044 seconds
 
-Also in this release is an alpha version of the new "gist" tool, which
-leverages the OpenCV library to create one page summaries of the
-geometric information present in .g files.
-
 * add 'brep dump' subcommand to write out brep objects - Cliff Yapp
 * improve 'x' default behavior in MGED - Chris McGregor
 * fixed 'edcolor' and 'color -e' on Windows - Chris McGregor