Fix test setup Function to use order api

Fix test setup Function to use order api

After ongoing issues resolving https://github.com/civicrm/civicrm-core/pull/14763 I have concluded the underlying
issue on the failing tests is the test setup. Specifically the use of 'partial_amount_to_pay' does not
create the correct underlying entities - it 'sort of' creates a payment without linking it to
the financial items.

These parameters are part of our first attempt at partial payments. I am removing them from the test here but
will deprecate later from other places in the code