Remove ExpandCSIVolumes feature gate

pkg/apis/core/types.go

@@ -1741,7 +1741,6 @@ type CSIPersistentVolumeSource struct {
 	// ControllerExpandSecretRef is a reference to the secret object containing
 	// sensitive information to pass to the CSI driver to complete the CSI
 	// ControllerExpandVolume call.
-	// This is an beta field and requires enabling ExpandCSIVolumes feature gate.
 	// This field is optional, and may be empty if no secret is required. If the
 	// secret object contains more than one secret, all secrets are passed.
 	// +optional