Revert "zbar: ghostscript was missing for zbar"

This reverts commit a906355b8ab404baa20dc167225d57e3120f067d.

Fixed imagemagick -lgs reference in .la file.

cc @garbas

pkgs/tools/graphics/zbar/default.nix

···
 x@{builderDefsPackage
   , imagemagickBig, pkgconfig, python, pygtk, perl, libX11, libv4l
-  , qt4, lzma, gtk2, ghostscript
+  , qt4, lzma, gtk2
   , ...}:
 builderDefsPackage
 (a :  

pkgs/top-level/all-packages.nix

···
     pygtk = lib.overrideDerivation pygtk (x: {
       gtk = gtk2;
     });
-    ghostscript = ghostscriptX;
   };
 
   zdelta = callPackage ../tools/compression/zdelta { };