Revert "cmake: also clean files generated from .in"

Cmake still doesn't know how te recreate these automatically..
That feature might be in 2.8.11:
http://public.kitware.com/Bug/view.php?id=13582
but we don't want to depend on bleeding edge cmake anyways.

This reverts commit 63a5170bfea37373a4a94075c571505d34e8e32a.

Conflicts:
	CMakeLists.txt
LIB-24: support generic platform (cmake)

We now don't just fail when we don't know the platform.
We build for the "generic" platform.
No disc access is available, but discid_put works just fine.