When a field is no longer read by any Spinnaker microservice, the field should be deprecated in Halyard so users know it is safe to remove from their halconfig.
To deprecate a field, annotate it with ValidForSpinnakerVersion, indicating
the first Spinnaker version in which the field is no longer necessary as the
upperBound. Optionally, supply a message indicating why the field is no
longer required as the tooHighMessage.
See the artifacts and artifactsRewrite fields in the Features class as
examples of deprecated fields.