Reverts #1795

We'd like to carry forward more information from vunnel (upstream of grype-db) to convey to grype DB consumers more details about the status and origin of the underlying data. #1795 started by adding a timestamp each each upstream provider was refreshed, a purely additive change, so it was added to the current v5 schema. However we've had reports of consumers that were adversely affected by this change, so we've decided to hold off on a change to the metadata.json datashape in the mean time. This will most likely be added as a separate file in a future change, and migrated back to the metadata.json when the DB schema is bumped -- but all of that will be finalized later.