scripts: remove kernel-ci loop infrastructure

Remove the now-unused kernel-ci loop testing scripts:

- Remove run_loop.sh from all workflows except reboot-limit
- Remove generic run_kernel_ci.sh script
- Remove kotd/run_kernel_ci_kotd.sh script and empty kotd directory

These scripts were part of the CONFIG_KERNEL_CI infrastructure that
has been replaced with workflow-specific implementations or better
testing approaches like SOAK_DURATION.

The reboot-limit workflow keeps its run_loop.sh as it now uses
internal loop configuration.

Generated-by: Claude AI
Signed-off-by: Luis Chamberlain <[email protected]>

Author: mcgrof