Removed unused imports.

tests/test_renderers.py

 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
-from django.conf.urls import patterns, url, include
+from django.conf.urls import url, include
 from django.core.cache import cache
 from django.db import models
 from django.test import TestCase

tests/test_testing.py

 # encoding: utf-8
 from __future__ import unicode_literals
-from django.conf.urls import patterns, url
+from django.conf.urls import url
 from django.contrib.auth.models import User
 from django.shortcuts import redirect
 from django.test import TestCase

tests/test_utils.py

 from __future__ import unicode_literals
 from django.core.exceptions import ImproperlyConfigured
-from django.conf.urls import patterns, url
+from django.conf.urls import url
 from django.test import TestCase
 from django.utils import six
 from rest_framework.utils.model_meta import _resolve_model