Cleaned-up configurations for ATLMCPROD-10458.
PreInclude for Simulation (with this then the DataRunNumber setting is no longer required): Campaigns/MC21SimulationLowMuRun.py
PreInclude for Digitization (with this then the preExec to set digitizationFlags.dataRunNumber
is no longer required): Campaigns/MC21NoPileUpLowMuRun.py
Tagging @kkrizka