Remove aggregated v2beta1 client-side usage

[Jefftree]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Remove client-go usage of aggregated discovery v2beta1 type. Server side change will be done in a separate PR since emulation version may be involved.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

pull-kubernetes-apidiff-client-go failure is expected as the beta type is dropped.

Does this PR introduce a user-facing change?

client-go will only query aggregated discovery using `apidiscovery.k8s.io/v2` and drop support for `apidiscovery.k8s.io/v2beta1`

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

/triage accepted

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Jefftree
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• staging/src/k8s.io/client-go/OWNERS

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[Jefftree]

/assign @jpbetz @seans3

[k8s-triage-robot]

This PR may require API review.

If so, when the changes are ready, complete the pre-review checklist and request an API review.

Status of requested reviews is tracked in the API Review project.

[k8s-ci-robot]

@Jefftree: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubernetes-apidiff-client-go	131b03b	link	false	/test pull-kubernetes-apidiff-client-go
pull-kubernetes-typecheck	131b03b	link	true	/test pull-kubernetes-typecheck
pull-kubernetes-conformance-kind-ga-only-parallel	131b03b	link	true	/test pull-kubernetes-conformance-kind-ga-only-parallel
pull-kubernetes-e2e-kind-ipv6	131b03b	link	true	/test pull-kubernetes-e2e-kind-ipv6
pull-kubernetes-integration	131b03b	link	true	/test pull-kubernetes-integration
pull-kubernetes-e2e-kind	131b03b	link	true	/test pull-kubernetes-e2e-kind
pull-kubernetes-e2e-gce	131b03b	link	true	/test pull-kubernetes-e2e-gce
pull-kubernetes-node-e2e-containerd	131b03b	link	true	/test pull-kubernetes-node-e2e-containerd
pull-kubernetes-unit	131b03b	link	true	/test pull-kubernetes-unit
pull-kubernetes-verify	131b03b	link	true	/test pull-kubernetes-verify

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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