py/obj: Convert make_new into a mp_obj_type_t slot.

Instead of being an explicit field, it's now a slot like all the other
methods.

This is a marginal code size improvement because most types have a make_new
(100/138 on PYBV11), however it improves consistency in how types are
declared, removing the special case for make_new.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/runtime.c

@@ -1076,7 +1076,6 @@ STATIC MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_checked_fun,
     MP_QSTR_function,
     MP_TYPE_FLAG_BINDS_SELF,
-    MP_TYPE_NULL_MAKE_NEW,
     call, checked_fun_call
     );