Remove delegation to RNode in Resource

[monopole]

The core data structure of kustomize is a list of resource.Resource.

A Resource includes raw data about a resource (what one would send to a cluster) plus ancillary data used by kustomize to globally transform resources (e.g. update name back references when names change).

To close #2506, enabling the closure of #1500, kustomize was switched from depending on apimachinery Unstructured types inside resource.Resource to the relatively new kyaml module and its RNode type. Many of the signatures maintained by Resource now simply delegate to RNode, and this delegation can now be removed as a cleanup to #2506.

At some later point (not to close this PR) assure that the ancillary data in Resource (outside the RNode) is sent to and re-captured from transformer subprocess (as the process might edit the information). One way to do this would be to solely use RNode (YAML) annotation reading and writing instead of Resource struct data members.