dataformfield_entrystate_entrystate::update_state() calls dataformfield_entrystate_entrystate::send_notifications() which calls the non-existing mod_dataform\pluginbase\dataformnotification::notify().

The notify method has been moved to mod_dataform\observer\notification::notify() which handles notifications on events and calls mod_dataform\observer\notification::send_message() for sending a message.