bpo-33251: Prevent ConfigParser.items returning items present in vars. (#6446)

* bpo-33251: ConfigParser.items no longer returns items present in vars.

Documentation for `ConfigParser.items()` states:
'Items present in vars no longer appear in the result.'

This fix aligns behaviour to that specified in the documentation.
diff --git a/Lib/test/test_configparser.py b/Lib/test/test_configparser.py
index 4d07203..87b811f 100644
--- a/Lib/test/test_configparser.py
+++ b/Lib/test/test_configparser.py
@@ -915,8 +915,7 @@
         self.check_items_config([('default', '<default>'),
                                  ('getdefault', '|<default>|'),
                                  ('key', '|value|'),
-                                 ('name', 'value'),
-                                 ('value', 'value')])
+                                 ('name', 'value')])
 
     def test_safe_interpolation(self):
         # See http://www.python.org/sf/511737
@@ -1093,8 +1092,7 @@
         self.check_items_config([('default', '<default>'),
                                  ('getdefault', '|%(default)s|'),
                                  ('key', '|%(name)s|'),
-                                 ('name', '%(value)s'),
-                                 ('value', 'value')])
+                                 ('name', '%(value)s')])
 
     def test_set_nonstring_types(self):
         cf = self.newconfig()