Use our existing drop-in, no-op decorator instead of redefining it.

Patch by Francisco Martin Brugue.
diff --git a/Lib/packaging/tests/test_pypi_xmlrpc.py b/Lib/packaging/tests/test_pypi_xmlrpc.py
index 682bd7b..b7b382d 100644
--- a/Lib/packaging/tests/test_pypi_xmlrpc.py
+++ b/Lib/packaging/tests/test_pypi_xmlrpc.py
@@ -3,18 +3,14 @@
 from packaging.pypi.xmlrpc import Client, InvalidSearchField, ProjectNotFound
 
 from packaging.tests import unittest
+from packaging.tests.support import fake_dec
 
 try:
     import threading
     from packaging.tests.pypi_server import use_xmlrpc_server
 except ImportError:
     threading = None
-    def use_xmlrpc_server():
-        def _use(func):
-            def __use(*args, **kw):
-                return func(*args, **kw)
-            return __use
-        return _use
+    use_xmlrpc_server = fake_dec
 
 
 @unittest.skipIf(threading is None, "Needs threading")