Issue #24254: Drop cls.__definition_order__.

Lib/types.py

@@ -25,11 +25,8 @@ CoroutineType = type(_c)
 _c.close()  # Prevent ResourceWarning
 
 class _C:
-    _nsType = type(locals())
     def _m(self): pass
 MethodType = type(_C()._m)
-# In CPython, this should end up as OrderedDict.
-_DefaultClassNamespaceType = _C._nsType
 
 BuiltinFunctionType = type(len)
 BuiltinMethodType = type([].append)     # Same as BuiltinFunctionType
@@ -88,7 +85,7 @@ def prepare_class(name, bases=(), kwds=None):
     if hasattr(meta, '__prepare__'):
         ns = meta.__prepare__(name, bases, **kwds)
     else:
-        ns = _DefaultClassNamespaceType()
+        ns = {}
     return meta, ns, kwds
 
 def _calculate_meta(meta, bases):