Cleanup py27 support

This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove python 2.7 stanza from setup.py

Change-Id: Ida5fd3abd77e507f50953c62eeb2490068eebcd0

setup.py

@@ -15,14 +15,6 @@
 
 import setuptools
 
-# In python < 2.7.4, a lazy loading of package `pbr` will break
-# setuptools if some other modules registered functions in `atexit`.
-# solution from: http://bugs.python.org/issue15881#msg170215
-try:
-    import multiprocessing  # noqa
-except ImportError:
-    pass
-
 setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
     pbr=True)