Draft: AthSimulationExternals LCG Fix, main branch (2024.02.28.)

Stopped AthSimulationExternals from looking for "LCG generator packages".

Nothing in AthSimulationExternals or AthSimulation depends on any "LCG generators". This means that an installed AthSimulation release doesn't install any of those (RPM) packages either. Not even the "LCG_generators_<platform>.txt" file that would come with the release. (As long as at least one generator package would be installed.)

This is to fix one component of the issues reported in ATLINFR-5262.

Note that this actually highlights a slightly deeper issue with how AtlasLCG works. 🤔 With this patch in, we'll get in trouble once/if AthSimulation does start depending on some generator package(s). At which point we'll need to make some slightly bigger changes in AtlasLCG. But for now this simple band-aid seemed the most pragmatic thing to do... (And just as I wrote this down, I realized that I could be doing things in a slightly better way as well... So let's mark this as a draft for now...)