Fix unreleased api change

Fix unreleased api change

An unreleased change adds the entity ids for membership to the return values.

However, on digging into further cleanup I realised that the entity ids are in
the line item array, along with other values which may or may not be useful,
and it's cleaner, more complete and more maintainable to return the line_items.

It requires an extra foreach loop in the calling code but
I don't see that as a downside.

We should change this in the rc so what is released is consistent

Test cover in testSubmitRecur & other tests in CRM_Member_Form_MembershipTest