Fix doctest's __all__.
diff --git a/Lib/doctest.py b/Lib/doctest.py
index 49e2fe6..0322612 100644
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -80,13 +80,11 @@
     'testmod',
     'testfile',
     'run_docstring_examples',
-    # 7. Tester
-    'Tester',
-    # 8. Unittest Support
+    # 7. Unittest Support
     'DocTestSuite',
     'DocFileSuite',
     'set_unittest_reportflags',
-    # 9. Debugging Support
+    # 8. Debugging Support
     'script_from_examples',
     'testsource',
     'debug_src',