code: public Completable removeProducts(List<Product> products) {
      List<Product> updatedShoppingCart = new ArrayList<>();
      updatedShoppingCart.addAll(itemsInShoppingCart.getValue());
      updatedShoppingCart.removeAll(products);
      itemsInShoppingCart.onNext(updatedShoppingCart);
      return Completable.complete();
    }
docs: Remove a list of Products from the shopping cart