fix ffm arena test

Author: madsodgaard

SwiftKitFFM/src/test/java/org/swift/swiftkit/ffm/AutoArenaTest.java

@@ -48,8 +48,6 @@ public void cleaner_releases_native_resource() {
     }
 
     private static class FakeSwiftInstance extends FFMSwiftInstance implements SwiftHeapObject {
-        private final AtomicBoolean $state$destroyed = new AtomicBoolean(false);
-
         public FakeSwiftInstance(AllocatingSwiftArena arena) {
             super(MemorySegment.NULL, arena);
         }
@@ -58,10 +56,5 @@ public FakeSwiftInstance(AllocatingSwiftArena arena) {
         public SwiftAnyType $swiftType() {
             return null;
         }
-
-        @Override
-        public AtomicBoolean $statusDestroyedFlag() {
-            return $state$destroyed;
-        }
     }
 }