Drop MC16-style DigitizationTests ART jobs
After !62318 (merged) MC16-style digitization jobs are effectively broken in 23.0 and master. As the MC20 campaign is the current recommended Run2 campaign, this merge request drops most MC16-style jobs and updates two to MC20-style configuration.
NB This MR only affects ART scripts, so will have no effect on the CI output.