[Test Improvement] Check whether the product is gone from the backend also

Problem/Motivation

Tests included here #2910740: Ajaxify the Remove from cart button are going to check visually that the product is gone from the cart. It would be better and more foolproof if it is checked whether the order item concerning the product is also gone from the backend (database).

Proposed resolution

Update the tests. The visual tests should be there, just add new tests that would check whether the order item is gone.

Also check that if not waited for ajax to complete, then the items are still in the backend.

Remaining tasks

Make sure that in the tests it checks whether the other product is still in the cart.

User interface changes

N/A

API changes

N/A

Data model changes

N/A