bpo-41521: Rename blacklist parameter to not_exported (GH-21824)

Rename "blacklist" parameter of test.support.check__all__() to
"not_exported".
diff --git a/Lib/test/test_smtpd.py b/Lib/test/test_smtpd.py
index d5d5abf..6303192 100644
--- a/Lib/test/test_smtpd.py
+++ b/Lib/test/test_smtpd.py
@@ -1003,12 +1003,11 @@
 
 class MiscTestCase(unittest.TestCase):
     def test__all__(self):
-        blacklist = {
+        not_exported = {
             "program", "Devnull", "DEBUGSTREAM", "NEWLINE", "COMMASPACE",
             "DATA_SIZE_DEFAULT", "usage", "Options", "parseargs",
-
         }
-        support.check__all__(self, smtpd, blacklist=blacklist)
+        support.check__all__(self, smtpd, not_exported=not_exported)
 
 
 if __name__ == "__main__":