Actually, it's a c++ Property of any given faction.

They changed the system so that settling on barren, etc. worlds no longer has a technology as prerequisite, but rather a property (CanColonizeExtremeWorld > 0). This is due to their XML prerequisites logic being incapable of handling OR-logic between different types of objects and their new RaceTrait for custom races that enables you to colonize extreme worlds right away from the start.

Since their system wouldn't support them setting the condition to "either have this tech or that trait", they instead set it to a new property and had both tech and trait increase that property instead.

And since that was a bit rushed in all the other fixes in the shortest time possible (let's be honest here, fixing crashes is a bit more important), they didn't catch that note. Oh well, it happens.