Discussed at
https://macadmins.slack.com/archives/C0214NELAE7/p1769719765777279
- The endpoints for marking a device as unmanaged and sending an
unmanage command were deprecated and no longer work. The endpoint for
looking up a device by serial number was also deprecated, so I've
proactively updated it.
- The whole story is now refactored and simplified.
- Also fixed a link in the `tines` README.
