Fix pages that reference removed API groups

Quite some resources have been moved out of the `extensions` API group
since 1.18; the `apps/v1beta1` and `apps/v1beta2` group versions are
also dropped. This PR updates the pages which still reference such API
groups or group versions.

content/en/docs/concepts/overview/kubernetes-api.md

@@ -25,8 +25,6 @@ The Kubernetes API lets you query and manipulate the state of objects in the Kub
 API endpoints, resource types and samples are described in the [API Reference](/docs/reference/kubernetes-api/).
 
 
-
-
 <!-- body -->
 
 ## API changes
@@ -87,7 +85,7 @@ Kubernetes implements an alternative Protobuf based serialization format for the
 
 To make it easier to eliminate fields or restructure resource representations, Kubernetes supports
 multiple API versions, each at a different API path, such as `/api/v1` or
-`/apis/extensions/v1beta1`.
+`/apis/rbac.authorization.k8s.io/v1alpha1`.
 
 Versioning is done at the API level rather than at the resource or field level to ensure that the
 API presents a clear, consistent view of system resources and behavior, and to enable controlling
@@ -157,14 +155,6 @@ The flag accepts comma separated set of key=value pairs describing runtime confi
 {{< note >}}Enabling or disabling groups or resources requires restarting the kube-apiserver and the
 kube-controller-manager to pick up the `--runtime-config` changes.{{< /note >}}
 
-## Enabling specific resources in the extensions/v1beta1 group
-
-DaemonSets, Deployments, StatefulSet, NetworkPolicies, PodSecurityPolicies and ReplicaSets in the `extensions/v1beta1` API group are disabled by default.
-For example: to enable deployments and daemonsets, set
-`--runtime-config=extensions/v1beta1/deployments=true,extensions/v1beta1/daemonsets=true`.
-
-{{< note >}}Individual resource enablement/disablement is only supported in the `extensions/v1beta1` API group for legacy reasons.{{< /note >}}
-
 ## Persistence
 
 Kubernetes stores its serialized state in terms of the API resources by writing them into