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/workloads/controllers/deployment.md

@@ -1155,10 +1155,6 @@ created Pod should be ready without any of its containers crashing, for it to be
 This defaults to 0 (the Pod will be considered available as soon as it is ready). To learn more about when
 a Pod is considered ready, see [Container Probes](/docs/concepts/workloads/pods/pod-lifecycle/#container-probes).
 
-### Rollback To
-
-Field `.spec.rollbackTo` has been deprecated in API versions `extensions/v1beta1` and `apps/v1beta1`, and is no longer supported in API versions starting `apps/v1beta2`. Instead, `kubectl rollout undo` as introduced in [Rolling Back to a Previous Revision](#rolling-back-to-a-previous-revision) should be used.
-
 ### Revision History Limit
 
 A Deployment's revision history is stored in the ReplicaSets it controls.

content/en/docs/concepts/workloads/controllers/garbage-collection.md

@@ -111,12 +111,6 @@ To control the cascading deletion policy, set the `propagationPolicy`
 field on the `deleteOptions` argument when deleting an Object. Possible values include "Orphan",
 "Foreground", or "Background".
 
-Prior to Kubernetes 1.9, the default garbage collection policy for many controller resources was `orphan`.
-This included ReplicationController, ReplicaSet, StatefulSet, DaemonSet, and
-Deployment. For kinds in the `extensions/v1beta1`, `apps/v1beta1`, and `apps/v1beta2` group versions, unless you 
-specify otherwise, dependent objects are orphaned by default. In Kubernetes 1.9, for all kinds in the `apps/v1` 
-group version, dependent objects are deleted by default.
-
 Here's an example that deletes dependents in background:
 
 ```shell