Delete the obsolete legacy `TriggerFlags.configurationSourceList` flag
and related configuration code.

Also delete the following flags:
  -`readLVL1FromJSON`: was only required during the Run-3
  migration while we had to support old and new menus
 - `useRun1CaloEnergyScale`: not used anymore as we don't simulate past
 triggers in this release
 - `doLVL1`: already migrated to new-style `ConfigFlag`
 - `doNavigationSlimming`: migrate remaining code to new-style flag