Remove workaround for Python 2.6 wrt OrderedDict

collections.OrderedDict was added to Python starting with 2.7. As
django-import-export only supports Python 2.7+ or Python 3.3+, can
safely rely on the stdlib version of OrderedDict.

import_export/resources.py

@@ -3,6 +3,7 @@
 import functools
 import tablib
 import traceback
+from collections import OrderedDict
 from copy import deepcopy
 
 from diff_match_patch import diff_match_patch
@@ -41,11 +42,6 @@
 except ImportError:
     from django.utils.encoding import force_unicode as force_text
 
-try:
-    from collections import OrderedDict
-except ImportError:
-    from django.utils.datastructures import SortedDict as OrderedDict
-
 # Set default logging handler to avoid "No handler found" warnings.
 import logging  # isort:skip
 try:  # Python 2.7+

import_export/results.py

@@ -1,9 +1,6 @@
 from __future__ import unicode_literals
 
-try:
-    from collections import OrderedDict
-except ImportError:
-    from django.utils.datastructures import SortedDict as OrderedDict
+from collections import OrderedDict
 
 from tablib import Dataset