Remove old RHCOS and FCOS metadata (not stream metadata)

In openshift/enhancements#679
we landed support for a stream metadata format already used
by FCOS and now by RHCOS/OCP consumers to find the bootimages.

We kept the old metadata because the UPI CI jobs used it.
In openshift/release#17482 I tried
to port the UPI CI jobs, but ran into huge levels of technical debt.

As best I can tell, the UPI CI jobs are not running on this repo
now and are likely broken for other reasons.

Let's remove the old data and avoid the confusing duplication.
Anyone who goes to work on the UPI CI jobs and sanitizes things
should be able to pick up the work to port to stream metadata
relatively easily.