gst_all_1.gst-plugins-bad: disable zbar by default

gst-plugins-bad by default used to pull in gtk3 and qtbase and qtx11extras because of the default dependency on zbar.
As zbar is a rarely needed gstreamer plugin, this unnecessarily
increased the closure size.
I am only aware of gnome-keysign actually using the zbar plugin, so that
uses a zbar-enabled gst-plugins-bad.

closes #84845

pkgs/development/libraries/gstreamer/bad/default.nix

@@ -10,7 +10,7 @@
 , gst-plugins-base
 , orc
 , gobject-introspection
-, enableZbar ? true
+, enableZbar ? false
 , faacSupport ? false
 , faac ? null
 , faad2

pkgs/tools/security/gnome-keysign/default.nix

@@ -53,7 +53,7 @@ python3.pkgs.buildPythonApplication rec {
     gst_all_1.gstreamer
     gst_all_1.gst-plugins-base
     (gst_all_1.gst-plugins-good.override { gtkSupport = true; })
-    gst_all_1.gst-plugins-bad # for zbar plug-in
+    (gst_all_1.gst-plugins-bad.override { enableZbar = true; }) # for zbar plug-in
   ];
 
   propagatedBuildInputs = with python3.pkgs; [