treewide: use scons setup hook

Lots of packages can use it. Here is the list:

- jackmix
- klick
- mixx
- nova-filters
- rhvoice
- giv
- mypaint
- swift-im
- bombono
- mapnik
- serf
- nuitka
- pyexiv2
- godot
- hammer
- toluapp
- btanks
- dxx-rebirth
- endless-sky
- globulation
- the-powder-toy
- fceux
- gpsd
- mongodb
- rippled
- mariadb
- lprof

pkgs/applications/graphics/mypaint/default.nix

@@ -26,10 +26,7 @@ in stdenv.mkDerivation rec {
 
   propagatedBuildInputs = [ numpy ];
 
-  buildPhase = "scons prefix=$out";
-
-  installPhase = ''
-    scons prefix=$out install
+  postInstall = ''
     sed -i -e 's|/usr/bin/env python2.7|${python}/bin/python|' $out/bin/mypaint
   '';