Get rid of distribute

Hello, about a year ago distribute was merged back into setuptools, so there is no more need to depend on it instead of setuptools. There is the details: 
https://pythonhosted.org/setuptools/merge.html

For FreeBSD we hold this change as local patch for py-amf port, and it will be great if we can drop it. Here is the similar patch in FreeBSD py-amf port:
https://svnweb.freebsd.org/ports/head/www/py-amf/files/patch-setup.py?revision=335046&view=co