Remove polyfill for Python < 2.7

test/test_dataset.py

@@ -1,14 +1,11 @@
 # coding: utf-8
 from __future__ import unicode_literals
 
+from collections import OrderedDict
 import os
 import unittest
 from datetime import datetime
 
-try:
-    from collections import OrderedDict
-except ImportError:  # pragma: no cover
-    from ordereddict import OrderedDict  # Python < 2.7 drop-in
 
 from sqlalchemy import FLOAT, INTEGER, TEXT
 from sqlalchemy.exc import IntegrityError, SQLAlchemyError, ArgumentError