Fix test_wsgiref execution from the test module.

Lib/test/test_wsgiref.py

-from __future__ import nested_scopes    # Backward compat for 2.1
 from unittest import TestCase
 from wsgiref.util import setup_testing_defaults
 from wsgiref.headers import Headers
 from wsgiref.handlers import BaseHandler, BaseCGIHandler
 from wsgiref import util
 from wsgiref.validate import validator
-from wsgiref.simple_server import WSGIServer, WSGIRequestHandler, demo_app
+from wsgiref.simple_server import WSGIServer, WSGIRequestHandler
 from wsgiref.simple_server import make_server
 from io import StringIO, BytesIO, BufferedReader
 from socketserver import BaseServer
@@ -14,8 +13,8 @@ from platform import python_implementation
 import os
 import re
 import sys
+import unittest
 
-from test import support
 
 class MockServer(WSGIServer):
     """Non-socket HTTP server"""