Merge #243

243: Complete migration of kernel target r=stlankes a=mkroening

I noticed this due to [failing docs CI](https://github.com/hermitcore/libhermit-rs/runs/2889060428

).
The rename began in 18dd15f5.
It seems that the repository-local json target specifications are not used, so I removed those.

Co-authored-by: Martin Kröning <mkroening@posteo.net>