DigitizationTests ART: Drop obsolete test_Digi_tf_mc15_2015_heavy_ion.sh job (ATLASSIM-7059)
This MR just removes an obsolete ART script - it will have no effect on the CI output.
Tagging @zhubacek
This MR just removes an obsolete ART script - it will have no effect on the CI output.
Tagging @zhubacek