Register and enable defaultpreemption plugin

- Enable defaultpreemption as a PostFilter plugin
- Remote legacy hard-coded preemption logic

pkg/scheduler/eventhandlers.go

@@ -30,7 +30,6 @@ import (
 	coreinformers "k8s.io/client-go/informers/core/v1"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/kubernetes/pkg/features"
-	kubefeatures "k8s.io/kubernetes/pkg/features"
 	"k8s.io/kubernetes/pkg/scheduler/internal/queue"
 	"k8s.io/kubernetes/pkg/scheduler/profile"
 )
@@ -467,11 +466,6 @@ func addAllEventHandlers(
 			AddFunc: sched.onStorageClassAdd,
 		},
 	)
-
-	// TODO(Huang-Wei): remove this hack when defaultpreemption plugin is enabled.
-	if utilfeature.DefaultFeatureGate.Enabled(kubefeatures.PodDisruptionBudget) {
-		informerFactory.Policy().V1beta1().PodDisruptionBudgets().Lister()
-	}
 }
 
 func nodeSchedulingPropertiesChange(newNode *v1.Node, oldNode *v1.Node) string {