bpo-32911: Revert bpo-29463. (GH-7121)

Remove the docstring attribute of AST types and restore docstring
expression as a first stmt in their body.

Co-authored-by: INADA Naoki <methane@users.noreply.github.com>
diff --git a/Lib/test/test_opcodes.py b/Lib/test/test_opcodes.py
index 8af098f..6806c61 100644
--- a/Lib/test/test_opcodes.py
+++ b/Lib/test/test_opcodes.py
@@ -27,7 +27,7 @@
             with open(ann_module.__file__) as f:
                 txt = f.read()
             co = compile(txt, ann_module.__file__, 'exec')
-            self.assertEqual(co.co_firstlineno, 8)
+            self.assertEqual(co.co_firstlineno, 6)
         except OSError:
             pass