Draft: chore: deletes the unused metrics package

Based on my searches, I've been unable to find any users of this package. As such, I'm opting to remove it so that we can be more intentional about how any prospective metrics packages would look in the future.

Search: https://gitlab.com/search?group_id=9970&scope=blobs&search=labkit%2Fcorrelation%2Fmetrics