Drop MC16-style DigitizationTests ART jobs

Merged John Derek Chapman requested to merge jchapman/athena:DropMC16DigiART_23.0 into 23.0

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.

Tagging @zhubacek and @tadej

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