Remove getConfig helper function

An expression like ‘getConfig [ "cabal" "libraryProfiling" ] false’
can be written more concisely as ‘config.cabal.libraryProfiling or false’.

pkgs/games/oilrush/default.nix

@@ -1,11 +1,12 @@
-{ stdenv, getConfig, fetchurl, libX11, libXext, libXinerama, libXrandr
+{ stdenv, config, fetchurl, libX11, libXext, libXinerama, libXrandr
 , libXrender, fontconfig, freetype, openal }:
+
 stdenv.mkDerivation {
   name = "oilrush";
   src = 
   let
-    url = getConfig [ "oilrush" "url" ] null;
-    sha256 = getConfig [ "oilrush" "sha256" ] null;
+    url = config.oilrush.url or null;
+    sha256 = config.oilrush.sha256 or null;
   in
     assert url != null && sha256 != null;
     fetchurl { inherit url sha256; };