Remove deprecated admission interfaces from API types

[nrb]

controller-runtime has removed the admission.Defaulter and admission.Validator interfaces as of v0.20.0 (kubernetes-sigs/controller-runtime#2877)

cluster-api v1.10 uses a version of controller-runtime that no longer has these present.

Looking through related PR history, CAPI has provided an implementer's guide for transitioning these interfaces out of API packages. https://cluster-api.sigs.k8s.io/developer/providers/getting-started/implement-api-types#registering-apis-in-the-scheme

There's also some prior art in how CAPI itself removed these here: kubernetes-sigs/cluster-api#9045

[nrb]

/triage accepted

[nrb]

I think we'll want to tackle this independently of the CAPI bump, so we can contain the scope of the changes.

[damdo]

Some examples on how to do this can also be found on CAPG's PR: https://github.com/kubernetes-sigs/cluster-api-provider-gcp/pull/1459/files

[k8s-triage-robot]

This issue is labeled with priority/critical-urgent but has not been updated in over 30 days, and should be re-triaged.
Critical-urgent issues must be actively worked on as someone's top priority right now.

You can:

• Confirm that this issue is still relevant with /triage accepted (org members only)
• Deprioritize it with /priority {important-soon, important-longterm, backlog}
• Close this issue with /close

For more details on the triage process, see https://www.kubernetes.dev/docs/guide/issue-triage/

/remove-triage accepted

[nrb]

/triage accepted
/lifecycle frozen