Drop the support for CRI v1alpha2

[AkihiroSuda]

cri-dockerd/core/service_alpha.go

Line 25 in 9a8a9fe

runtimeapi_alpha "k8s.io/cri-api/v1alpha2/pkg/apis/runtime/v1alpha2"

Kubernetes has dropped the support for CRI v1alpha2 in Kubernetes v1.26:

• Remove CRI v1alpha2 kubernetes/kubernetes#110618

v1.25, the last release to support v1alpha2, has already reached the EOL: https://kubernetes.io/releases/patch-releases/#non-active-branch-history

So I guess cri-dockerd should be ready to drop it too?

[afbjorklund]

As long as it is documented (and something like 0.4?), I think the feature can be removed also from cri-dockerd...

Previously the versioning of tools like crictl was unclear, and thus many tried to use them with e.g. new containerd and failing. But now the release of cri-tools and cni-plugins has been bundled with the kubeadm installation, so that users need to upgrade their CRI and CNI with their k8s installation. There was already the issue of cri-dockerd not supporting k8s versions before 1.24, where dockershim should be used instead. But I think* 1.24-1.26 should support CRI v1?

* looking at for instance the https://containerd.io/releases/#kubernetes-support table, where it says "1.23+"

https://kubernetes.io/blog/2021/12/07/kubernetes-1-23-release-announcement/#container-runtime-interface-cri-v1-is-default