Remove optional setuptools import.

We don't rely on any setuptools features for python2 builds, and the
optional import makes our builds depend on the environment in subtle
ways (egg-info directories, etc).

setup.py

@@ -16,12 +16,6 @@
 
 import distutils.core
 import sys
-# Importing setuptools adds some features like "setup.py develop", but
-# it's optional so swallow the error if it's not there.
-try:
-    import setuptools
-except ImportError:
-    pass
 
 kwargs = {}