avm2: Fix QName's prototype

core/src/avm2/globals/QName.as

@@ -1,6 +1,8 @@
 package {
     [Ruffle(InstanceAllocator)]
     public final class QName {
+        public static const length = 2;
+        
         public function QName(uri:* = undefined, localName:*=undefined) {
             this.init(uri, localName)
         }
@@ -19,12 +21,7 @@ package {
             var self:QName = this;
             return self.AS3::toString();
         }
-        prototype.valueOf = function():QName {
-            var self:QName = this;
-            return self.AS3::valueOf();
-        }
 
         prototype.setPropertyIsEnumerable("toString", false);
-        prototype.setPropertyIsEnumerable("valueOf", false);
     }
-}
+}