* Remove code related to RHEL versions and not interesting in Fedora.
* Remove or simplify some architecture-specific code because Fedora CI
aims at x86_64 only.
* Remove some older and commented out experiments.
Sanity/rebuild-kernel-and-reboot is imported from RHEL's
tests/binutils/Sanity/rebuild-kernel-and-reboot (as of commit c5bc77c).
It needs some adaptations first before running in Fedora.