Minor change to setup.py (0.8.4 release)

This removes some some (apparently) `distribute` specific stuff. 

Background:
The python packages `setuptools` and `distribute` re-merged, and `distribute` seems to disappear from standard environments and package managers. The removed code causes the installation script to fail in such environments.

I guess this issue will disappear in a future 0.9.x release, as it uses a different (f2py based) setup.py script. Not sure what is the planing for *possible* 0.8.x bug fix releases. If such a release would use the *traditional* `setup.py` this fix might become relevant.