set-image sets conversion for web hook in CRD resource even if no web hook is setup

[henderiw]

Expected behavior

Was asked by John to create an Issue No conversion is added in CRD resource. The consequence is that by applying this CRD onto the cluster fails

  conversion:
    webhook:
      clientConfig:
        service:
          namespace: ndd-system

Actual behavior

when set-namespace is used the following lines are added to the CRD resource

  conversion:
    webhook:
      clientConfig:
        service:
          namespace: ndd-system

Information

the following lines on a Kpt Package that has a CRD resource

- image: gcr.io/kpt-fn/set-namespace:v0.4.1
  configMap:
    namespace: xxx

Steps to reproduce the behavior