Capacity is not restored for replaced out OrderItems when an Order's OrderItems are replaced

[lukehesluke]

Assumption: When an Order's OrderItems are replaced, Opportunities which were previously in the Order but have been replaced OUT should have their capacity restored in the Opportunity feed

Here's an example test run demonstrating that this does not happen when using ReplacementSimulateAction:

seller-requested-replacement_book-and-seller-replace-items_OpenBookingSimpleFlow_ScheduledSession.md

The converse of this is: If a new Opportunity gets replaced IN to an Order, it's capacity should then decrease. I haven't tested this yet, but I expect that it will also fail in RefImpl

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This was revealed while working on this Test Suite issue: openactive/openactive-test-suite#460