Automatic merge from submit-queue (batch tested with PRs 63151, 63795, 63553, 64068, 64113). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
kubeadm: Remove .AuthorizationModes in the v1alpha2 API
**What this PR does / why we need it**:
Now that we have https://github.com/kubernetes/kubernetes/pull/63879, we don't actually need to have `:AuthorizationModes` in our API anymore. This PR removes support for `.AuthorizationModes` in the v1alpha2 API, but keeps an upgrade path available (automatic conversion) from the v1alpha1 version.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Part of kubernetes/community#2131
**Special notes for your reviewer**:
Depends on:
- [x] https://github.com/kubernetes/kubernetes/pull/63879
- [x] https://github.com/kubernetes/kubernetes/pull/63917
**Release note**:
```release-note
[action required] kubeadm: Support for `.AuthorizationModes` in the kubeadm v1alpha2 API has been removed. Instead, you can use the `.APIServerExtraArgs` and `.APIServerExtraVolumes` fields to achieve the same effect. Files using the v1alpha1 API and setting this field will be automatically upgraded to this v1alpha2 API and the information will be preserved.
```
@kubernetes/sig-cluster-lifecycle-pr-reviews @liztio
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