boost: Kill unnecessary 'lib' output

This was split in somewhere pre-2014 without the current infra which
automates parts of this, in particular the output propagation.

pkgs/development/libraries/audio/lvtk/default.nix

@@ -20,7 +20,7 @@ stdenv.mkDerivation rec {
   configurePhase = ''
     python waf configure --prefix=$out \
       --boost-includes="${boost.dev}/include" \
-      --boost-libs="${boost.lib}/lib"
+      --boost-libs="${boost.out}/lib"
   '';
 
   buildPhase = "python waf";