CiviAccounts api tests broken on create contribution with nested line items

Define flag which causes contribution create api to bypass creation of default line_item record:

skipLineItem => 1

Default for this flag is FALSE, and is set in _contribution_create_spec

Update api_v3_ContributionTest which were using use_default_price_set=0 flag so they set the new skipLineItem flag to 1. This should allow those failing tests to succeed again.

— Original Post —
Not sure exactly the correct behaviour but the original api set up determined that it should be possible to create a contribution with line items by chaining them - per test

ContributionTest.php::testCreateContributionChainedLineItems

This now fails because an extra line item is created. There are a bunch of other tests on the same class which seem intended to test CiviAccounts API behaviour that has either changed or is broken.

I think it's important that it is possible to create a contribution with specified line items - even if the approach of using Chaining to achieve that isn't retained.