Merge pull request #40000 from jsafrane/storage-ga-remove-alpha

Automatic merge from submit-queue

Remove alpha provisioning

This is the first part of https://github.com/kubernetes/features/issues/36

@kubernetes/sig-storage-misc 

**Release note**:
```release-note
Alpha version of dynamic volume provisioning is removed in this release. Annotation
"volume.alpha.kubernetes.io/storage-class" does not have any special meaning. A default storage class
and  DefaultStorageClass admission plugin can be used to preserve similar behavior of Kubernetes cluster,
see https://kubernetes.io/docs/user-guide/persistent-volumes/#class-1 for details.
```

cmd/kube-controller-manager/app/controllermanager.go

@@ -472,14 +472,9 @@ func StartControllers(controllers map[string]InitFunc, s *options.CMServer, root
 		glog.Infof("Will not configure cloud provider routes for allocate-node-cidrs: %v, configure-cloud-routes: %v.", s.AllocateNodeCIDRs, s.ConfigureCloudRoutes)
 	}
 
-	alphaProvisioner, err := NewAlphaVolumeProvisioner(cloud, s.VolumeConfiguration)
-	if err != nil {
-		return fmt.Errorf("an backward-compatible provisioner could not be created: %v, but one was expected. Provisioning will not work. This functionality is considered an early Alpha version.", err)
-	}
 	params := persistentvolumecontroller.ControllerParameters{
 		KubeClient:                clientBuilder.ClientOrDie("persistent-volume-binder"),
 		SyncPeriod:                s.PVClaimBinderSyncPeriod.Duration,
-		AlphaProvisioner:          alphaProvisioner,
 		VolumePlugins:             ProbeControllerVolumePlugins(cloud, s.VolumeConfiguration),
 		Cloud:                     cloud,
 		ClusterName:               s.ClusterName,