bpo-40275: Use new test.support helper submodules in tests (GH-21452)

diff --git a/Lib/test/test_multibytecodec.py b/Lib/test/test_multibytecodec.py
index 3cf5d7b..7c3b67f 100644
--- a/Lib/test/test_multibytecodec.py
+++ b/Lib/test/test_multibytecodec.py
@@ -4,7 +4,8 @@
 #
 
 from test import support
-from test.support import TESTFN
+from test.support import os_helper
+from test.support.os_helper import TESTFN
 import unittest, io, codecs, sys
 import _multibytecodec
 
@@ -57,7 +58,7 @@
                 code = '# coding: {}\n'.format(enc)
                 exec(code)
         finally:
-            support.unlink(TESTFN)
+            os_helper.unlink(TESTFN)
 
     def test_init_segfault(self):
         # bug #3305: this used to segfault
@@ -296,7 +297,7 @@
             finally:
                 f.close()
         finally:
-            support.unlink(TESTFN)
+            os_helper.unlink(TESTFN)
 
 class Test_StreamWriter(unittest.TestCase):
     def test_gb18030(self):