Fixed isolation of test_filename_traversal_upload().

shutil.rmtree(MEDIA_ROOT) is already called as a class cleanup.

tests/file_uploads/tests.py

@@ -624,7 +624,6 @@ class FileUploadTests(TestCase):
 
     def test_filename_traversal_upload(self):
         os.makedirs(UPLOAD_TO, exist_ok=True)
-        self.addCleanup(shutil.rmtree, MEDIA_ROOT)
         tests = [
             '../test.txt',
             '../test.txt',