8316144: Remove unused field jdk.internal.util.xml.impl.XMLStreamWriterImpl.Element._Depth

Reviewed-by: lancea, joehw

Author: Andrey Turbanov

src/java.base/share/classes/jdk/internal/util/xml/impl/XMLStreamWriterImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -603,10 +603,6 @@ protected static class Element {
          * the parent element
          */
         protected Element _parent;
-        /**
-         * The size of the stack.
-         */
-        protected short _Depth;
         /**
          * indicate if an element is an empty one
          */