Stopped using django.utils.unittest in the test suite.

Refs #20680.

tests/utils_tests/test_http.py

@@ -1,12 +1,12 @@
 from datetime import datetime
 import sys
+import unittest
 
 from django.http import HttpResponse, utils
 from django.test import RequestFactory
 from django.utils.datastructures import MultiValueDict
 from django.utils import http
 from django.utils import six
-from django.utils import unittest
 
 
 class TestUtilsHttp(unittest.TestCase):