bpo-40275: Use new test.support helper submodules in tests (GH-21219)

diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index 7675a97..793c99a 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -216,7 +216,7 @@
             # regex to match 'test_builtin' in line:
             # '0:00:00 [  4/400] test_builtin -- test_dict took 1 sec'
             regex = re.compile(r'\btest_[a-zA-Z0-9_]+\b')
-            with open(os.path.join(support.SAVEDCWD, self.ns.fromfile)) as fp:
+            with open(os.path.join(os_helper.SAVEDCWD, self.ns.fromfile)) as fp:
                 for line in fp:
                     line = line.split('#', 1)[0]
                     line = line.strip()
@@ -559,7 +559,7 @@
         for k, v in totals.items():
             root.set(k, str(v))
 
-        xmlpath = os.path.join(support.SAVEDCWD, self.ns.xmlpath)
+        xmlpath = os.path.join(os_helper.SAVEDCWD, self.ns.xmlpath)
         with open(xmlpath, 'wb') as f:
             for s in ET.tostringlist(root):
                 f.write(s)
@@ -597,7 +597,7 @@
             test_cwd = 'test_python_worker_{}'.format(pid)
         else:
             test_cwd = 'test_python_{}'.format(pid)
-        test_cwd += support.FS_NONASCII
+        test_cwd += os_helper.FS_NONASCII
         test_cwd = os.path.join(self.tmp_dir, test_cwd)
         return test_cwd
 
@@ -609,10 +609,10 @@
         for name in glob.glob(path):
             if os.path.isdir(name):
                 print("Remove directory: %s" % name)
-                support.rmtree(name)
+                os_helper.rmtree(name)
             else:
                 print("Remove file: %s" % name)
-                support.unlink(name)
+                os_helper.unlink(name)
 
     def main(self, tests=None, **kwargs):
         self.parse_args(kwargs)
@@ -629,7 +629,7 @@
             # Run the tests in a context manager that temporarily changes the CWD
             # to a temporary and writable directory. If it's not possible to
             # create or change the CWD, the original CWD will be used.
-            # The original CWD is available from support.SAVEDCWD.
+            # The original CWD is available from os_helper.SAVEDCWD.
             with os_helper.temp_cwd(test_cwd, quiet=True):
                 # When using multiprocessing, worker processes will use test_cwd
                 # as their parent temporary directory. So when the main process