Remove workaround for issue with older python versions.

Author: gizmoguy

setup.py

@@ -14,12 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# a bug workaround.  http://bugs.python.org/issue15881
-try:
-    import multiprocessing
-except ImportError:
-    pass
-
 import setuptools
 import ryu.hooks