Geant4 Without VecGeom, master branch (2022.04.20.)

Updated Geant4 to build without VecGeom once more.

@jchapman, @mbandier, please have a look! I was not entirely sure whether -DGEANT4_USE_USOLIDS:STRING=CONS;POLYCONE should be removed. But since it was added in !916 (merged), this seemed like the way to go.

Later on we could add a cache variable like ATLAS_BUILD_GEANT4_WITH_VECGEOM to select how G4 would build. But I didn't want to complicate things further in this MR.

Thanks @akraszna! - That looks right to me, but @mbandier and @bmorgan are the real experts here.

Let's just go ahead then...

mentioned in commit 20aa17b3

merged