Fix reference to missing utility function, which is not more than an alias to...

Fix reference to missing utility function, which is not more than an alias to CPython's "PyObject_GenericGetAttr" in the limited API case.

Cython/Compiler/TypeSlots.py

@@ -498,7 +498,7 @@ class SyntheticSlot(InternalMethodSlot):
 
     def spec_value(self, scope):
         if self.slot_name == "tp_getattro" and not scope.defines_any_special(self.user_methods):
-            return "__Pyx_PyObject_GenericGetAttr"
+            return "PyObject_GenericGetAttr"
         return self.slot_code(scope)