bpo-40275: Use new test.support helper submodules in tests (GH-20849)

diff --git a/Lib/test/libregrtest/runtest.py b/Lib/test/libregrtest/runtest.py
index 9338b28..e46cc31 100644
--- a/Lib/test/libregrtest/runtest.py
+++ b/Lib/test/libregrtest/runtest.py
@@ -11,6 +11,8 @@
 import unittest
 
 from test import support
+from test.support import import_helper
+from test.support import os_helper
 from test.libregrtest.refleak import dash_R, clear_caches
 from test.libregrtest.save_env import saved_test_environment
 from test.libregrtest.utils import format_duration, print_warning
@@ -216,7 +218,7 @@
     abstest = get_abs_module(ns, test_name)
 
     # remove the module from sys.module to reload it if it was already imported
-    support.unload(abstest)
+    import_helper.unload(abstest)
 
     the_module = importlib.import_module(abstest)
 
@@ -313,7 +315,7 @@
     # since if a test leaves a file open, it cannot be deleted by name (while
     # there's nothing we can do about that here either, we can display the
     # name of the offending test, which is a real help).
-    for name in (support.TESTFN,):
+    for name in (os_helper.TESTFN,):
         if not os.path.exists(name):
             continue