drop rpm-ostree-base-db

[cgwalters]

I've been battling rpm-ostree-base-db and container layering. I did #5249 which helps, but it's still really not enough because ostree will end up re-hardlinking it all.

I think we need to just get rid of it. For the package layering case we should be able to just check out the rpmdb from the base commit? I don't know why we didn't do that originally.

[jlebon]

For the package layering case we should be able to just check out the rpmdb from the base commit? I don't know why we didn't do that originally.

From what I remember, we did do that originally, but it's more expensive than just querying from the base rpmdb you already have in your deployment root when all you want to do is an upgrade check. We do gracefully fallback though, so it's fine if a rechunked image doesn't have it. (And it wouldn't make sense to have it since the base rpmdb from the client's point of view includes all layered packages. So either we don't have it at all, or we do but it still matches the canonical rpmdb, but the latter would require postprocessing that doesn't seem worth it.)