Fixed installation with recent setuptools.

These lines were introduced here: https://github.com/nltk/nltk/commit/1ecbd2edc32db24b4e6c7dd8555d0b89c668f041
It seems they fix an issue with .svn folders. We use git now,
there are no .svn folders.

See also: http://stackoverflow.com/questions/1129180/how-can-i-make-setuptools-ignore-subversion-inventory

setup.py

@@ -29,13 +29,6 @@ with open(version_file) as fh:
 # setuptools
 from setuptools import setup, find_packages
 
-#
-# Prevent setuptools from trying to add extra files to the source code
-# manifest by scanning the version control system for its contents.
-#
-from setuptools.command import sdist
-del sdist.finders[:]
-
 setup(
     name = "nltk",
     description = "Natural Language Toolkit",