bpo-43916: Remove _disabled_new() function (GH-25745)

posix and _hashlib use the new Py_TPFLAGS_DISALLOW_INSTANTIATION
flag on their heap types, rather than using a custom tp_new function
(_disabled_new).
diff --git a/Lib/test/test_hmac.py b/Lib/test/test_hmac.py
index adf52ad..22d74e9 100644
--- a/Lib/test/test_hmac.py
+++ b/Lib/test/test_hmac.py
@@ -440,7 +440,7 @@ def test_withmodule(self):
     def test_internal_types(self):
         # internal types like _hashlib.C_HMAC are not constructable
         with self.assertRaisesRegex(
-            TypeError, "cannot create 'HMAC' instance"
+            TypeError, "cannot create '_hashlib.HMAC' instance"
         ):
             C_HMAC()