setdiscovery: drop the 'always' argument to '_updatesample' This argument exists because of the complex code flow in '_takequicksample'. It first gets the list of heads and then calls '_updatesample' on an empty initial sample and a size limit matching the differences between the number of heads and the target sample size. Finally the heads and the sample from '_updatesample' were added. To ensure this addition result had the exact target length, the code had to ensure no elements from the heads were added to the '_updatesample' content and therefore was passing this "always included set of heads". Instead we can just update the initial heads sample directly and use the final target size as target size for the update. This removes the need for this 'always' parameter to the '_updatesample' function The test are affected because different set building order results in different random sampling.