GeoModel Version Downgrade, master branch (2021.10.30.)

Reverted to GeoModel version ed3f6298.

As @tstreble reported today, the latest nightly does not allow packages like PixelGeoModelXml to be built on top of the nightly by themselves. I suspect that this is because of the switch from GeoModel hash ed3f6298 to 9668399f in the last nightly.

@tsulaia, @rbianchi, please start managing that project a whole lot better! You must start producing tagged releases of it. This hash-business can no longer stand! 😦 I'm having the worst time trying to identify what state of the repository each of those hashes mean. And they are clearly two extremely different versions...

GeoModelDev/GeoModel@ed3f6298...9668399f

For now I decided that going back to the "old version" was the way to go. I suspect that the "new version" provides GeoModelXml as well. And now that we still have GeoModelXml as part of this repository, a linking confusion (which is no doubt present in the nightly as well, we just didn't run into runtime issues because of it yet) shows up during the partial build that @tstreble tried to do. (And which I confirmed does indeed happen.)

At the same time cleaned up the version overrides in all the projects that needed it. Yeah, unfortunately the COOL/CORAL tag situation is also not great in the latest versions of atlas/atlasexternals...