Remove some unneeded code

* _kiwi.c is not needed anymore as it's content is exactly the same as the
  pygtk/pygobject versions found on Ubuntu 12.04 (and even older than it)
* The same applies for requiring to "Build a helper module for testing on gtk+
  versions lower than 2.10", as gtk versions lower than 2.10 are not found even
  on lucid (10.04)
Change-Id: I6965f33ac9d59f57b79b654beb07fb2390d12301