private static Stream<DeploymentInstanceSpec> flatten(Step step) {
        if (step instanceof DeploymentInstanceSpec) return Stream.of((DeploymentInstanceSpec) step);
        return step.steps().stream().flatMap(DeploymentSpec::flatten);
    }
Returns the deprecated elements used when creating this
config-model-api/src/main/java/com/yahoo/config/application/api/DeploymentSpec.java