bpo-40275: Move transient_internet from test.support to socket_helper (GH-19711)

diff --git a/Lib/test/test_robotparser.py b/Lib/test/test_robotparser.py
index 9d4764e..a3112b8 100644
--- a/Lib/test/test_robotparser.py
+++ b/Lib/test/test_robotparser.py
@@ -349,7 +349,7 @@
     @classmethod
     def setUpClass(cls):
         support.requires('network')
-        with support.transient_internet(cls.base_url):
+        with socket_helper.transient_internet(cls.base_url):
             cls.parser = urllib.robotparser.RobotFileParser(cls.robots_txt)
             cls.parser.read()