// The "todo" in this callback function represents the document that was found.
// It allows you to pass a reference back to the client in case they need a reference for some reason.
Todo.findByIdAndRemove(req.params.todoId, (err, todo) => {
    // As always, handle any potential errors:
    if (err) return res.status(500).send(err);
    // We'll create a simple object to send back with a message and the id of the document that was removed
    // You can really do this however you want, though.
    const response = {
        message: "Todo successfully deleted",
        id: todo._id
    };
    return res.status(200).send(response);
});