test: remove RetroactiveDefaultStorageClass feature gate

Since the feature is GA and locked to true, tests can no longer set it
to false. Cleaning up by removing all references to this feature gate
from tests.

Feature gate will be removed in v1.29.

test/integration/volume/persistent_volumes_test.go

@@ -19,9 +19,6 @@ package volume
 import (
 	"context"
 	"fmt"
-	utilfeature "k8s.io/apiserver/pkg/util/feature"
-	featuregatetesting "k8s.io/component-base/featuregate/testing"
-	"k8s.io/kubernetes/pkg/features"
 	"math/rand"
 	"os"
 	"strconv"
@@ -1045,7 +1042,6 @@ func TestPersistentVolumeMultiPVsDiffAccessModes(t *testing.T) {
 // assignment and binding of PVCs with storage class name set to nil or "" with
 // and without presence of a default SC.
 func TestRetroactiveStorageClassAssignment(t *testing.T) {
-	defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.RetroactiveDefaultStorageClass, true)()
 	s := kubeapiservertesting.StartTestServerOrDie(t, nil, []string{"--disable-admission-plugins=DefaultStorageClass"}, framework.SharedEtcd())
 	defer s.TearDownFn()
 	namespaceName := "retro-pvc-sc"