libungif: remove in favour of giflib

libungif was merged into giflib in 2006, and hasn't been updated
since.  All non-broken packages still using it build fine with giflib.

See <http://giflib.sourceforge.net/history.html>.

pkgs/development/libraries/pslib/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchurl, cmake, pkg-config, zlib, libpng, libjpeg, libungif, libtiff
+{ lib, stdenv, fetchurl, cmake, pkg-config, zlib, libpng, libjpeg, giflib, libtiff
 }:
 
 stdenv.mkDerivation rec {
@@ -12,7 +12,7 @@ stdenv.mkDerivation rec {
   };
 
   nativeBuildInputs = [ cmake pkg-config ];
-  buildInputs = [ zlib libpng libjpeg libungif libtiff ];
+  buildInputs = [ zlib libpng libjpeg giflib libtiff ];
 
   doCheck = true;