Removed useless warning silencing.

If memory serves, the corresponding warning disappeared in Django 1.7.

tests/httpwrappers/tests.py

@@ -6,7 +6,6 @@ import json
 import os
 import pickle
 import unittest
-import warnings
 
 from django.core.exceptions import SuspiciousOperation
 from django.core.serializers.json import DjangoJSONEncoder
@@ -18,7 +17,6 @@ from django.http import (QueryDict, HttpResponse, HttpResponseRedirect,
                          SimpleCookie, BadHeaderError, JsonResponse,
                          parse_cookie)
 from django.test import TestCase
-from django.utils.deprecation import RemovedInDjango18Warning
 from django.utils.encoding import smart_str, force_text
 from django.utils.functional import lazy
 from django.utils._os import upath
@@ -561,8 +559,6 @@ class FileCloseTests(TestCase):
         file1 = open(filename)
         r = HttpResponse(file1)
         self.assertFalse(file1.closed)
-        with warnings.catch_warnings():
-            warnings.simplefilter("ignore", RemovedInDjango18Warning)
         list(r)
         self.assertFalse(file1.closed)
         r.close()