rxvt_unicode: move defaults to package file

pkgs/applications/misc/rxvt_unicode/default.nix

···
-{ stdenv, fetchurl, makeDesktopItem, perlSupport, libX11, libXt, libXft,
+{ stdenv, fetchurl, makeDesktopItem, perlSupport ? true, libX11, libXt, libXft,
   ncurses, perl, fontconfig, freetype, pkgconfig, libXrender,
-  gdkPixbufSupport, gdk_pixbuf, unicode3Support }:
+  gdkPixbufSupport ? true, gdk_pixbuf, unicode3Support ? true }:
 
 let
   pname = "rxvt-unicode";

pkgs/top-level/all-packages.nix

···
   rxvt = callPackage ../applications/misc/rxvt { };
 
   # urxvt
-  rxvt_unicode = callPackage ../applications/misc/rxvt_unicode {
-    perlSupport = true;
-    gdkPixbufSupport = true;
-    unicode3Support = true;
-  };
+  rxvt_unicode = callPackage ../applications/misc/rxvt_unicode { };
 
   rxvt_unicode-with-plugins = callPackage ../applications/misc/rxvt_unicode/wrapper.nix {
     plugins = [