Remove the setuptools from requirements.txt to avoid a setuptools bug

setuptools has slightly backwards (or forward)-incompatible changes when
you update its version while still having libs installed with the old
one.

We only support python 3.4, which means the virtualenv comes with
setuptools and pip already, so we don’t require to reinstall it. At
worse, people will have to read the setup.py error message.

requirements.txt

@@ -1,4 +1,3 @@
-setuptools
 -e git+git://git.louiz.org/slixmpp#egg=slixmpp
 aiodns
 pygments