The system has been upgraded from the latest 1.6 release, whose configuration did to my knowledge not emit any warnings. Unfortunately nobody kept an upgrade log.
Given that these are builtin checks, I would have assumed that all of them would be migrated regardless of configuration context. Perhaps it’s only done on-demand.
I’m going to look at the source a bit deeper and try to see why these checks are migrated (perhaps it’s only done when some service uses it, and I can identify what the service configuration or discovery data is on that one).