Aligned with upstream branch

Sources/ManagedModels/SchemaCompatibility/CodableBox.swift

@@ -57,17 +57,13 @@ final class CodableBox<T: Codable>: NSObject, NSCopying {
     }
   }
 
-  final class Transformer: NSSecureUnarchiveFromDataTransformer {
+  final class Transformer: ValueTransformer {
 
     override class func transformedValueClass() -> AnyClass {
       CodableBox<T>.self
     }
     override class func allowsReverseTransformation() -> Bool { true }
 
-    override class var allowedTopLevelClasses: [AnyClass] {
-      [ CodableBox<T>.self, NSData.self ]
-    }
-
     override func transformedValue(_ value: Any?) -> Any? {
       // value is the box
       guard let value else { return nil }