platform/conf: Don't upgrade Ignition configs to 2.1.0-experimental
platform/conf: Don't upgrade Ignition configs to 2.1.0-experimental

We wanted to keep Ignition configs in their original schema, but were
using the unversioned config parser, which always converts configs to
the latest version. Switch to the versioned parser and correctly
interpret its return values.

dm0-/mantle,glevand/coreos--mantle,glevand/coreos--mantle,dm0-/mantle