chromium: Remove .py[co] files prior to building.

Thanks to @iElectric for the notification, although I'm not really sure
whether this will fix the following failed Hydra build:

http://hydra.nixos.org/build/17609086/nixlog/1/raw

The reason is that this failure doesn't happen on every build, but let's
see whether it will happen again now.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/applications/networking/browsers/chromium/common.nix

@@ -190,6 +190,7 @@ let
       libExecPath="${libExecPath}"
       python build/linux/unbundle/replace_gyp_files.py ${gypFlags}
       python build/gyp_chromium -f ninja --depth "$(pwd)" ${gypFlags}
+      find . -iname '*.py[co]' -delete
     '';
 
     buildPhase = let