Delete support for v1beta1 API w/o deleting the API itself.

[kgolab]

This makes v1beta1 objects handled via ConfigUnsupported condition, sample status of an v1beta1 object after the change:

status:
  conditions:
  - lastTransitionTime: 2019-03-12T13:13:01Z
    message: Label selector is no longer supported, please migrate to targetRef
    status: "True"
    type: ConfigUnsupported
  - lastTransitionTime: 2019-03-12T13:13:01Z
    status: "False"
    type: RecommendationProvided
  recommendation: {}

NOTE: This change is not flag-guarded since it didn't make sense to reuse beta1-api-deprecated flag and I didn't wanted to introduce another one. Please let me know if you want this otherwise.

PS. I haven't touched validation in this PR so one can still create v1beta1 objects. This will be part of a separate PR.

[kgolab]

/assign bskiba@

[bskiba]

/lgtm
/approve

[bskiba]

/approve

[k8s-ci-robot]

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