Remove em2 module.

I remove temporarily this module because it is not mature enough to be
included in the release. I've moved the code temporarily to
http://github.com/fseoane/em2 .

From: Fabian Pedregosa <fabian.pedregosa@inria.fr>

git-svn-id: https://scikit-learn.svn.sourceforge.net/svnroot/scikit-learn/trunk@389 22fbfee3-77ab-4535-9bad-27d1bd3bc7d8