allow AST objects to be like its subclasses

Lib/test/test_ast.py

@@ -195,9 +195,6 @@ class AST_Tests(unittest.TestCase):
         with self.assertRaises(AttributeError):
             x.vararg
 
-        with self.assertRaises(AttributeError):
-            ast.AST(lineno=2)
-
         with self.assertRaises(TypeError):
             # "_ast.AST constructor takes 0 positional arguments"
             ast.AST(2)