8243929: use @requires in serviceability/attach/AttachWithStalePidFile.java test

Reviewed-by: cjplummer

test/hotspot/jtreg/serviceability/attach/AttachWithStalePidFile.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2020, 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
@@ -30,6 +30,7 @@
  * @modules java.base/java.lang:open
  * @modules jdk.attach/sun.tools.attach
  * @library /test/lib
+ * @requires os.family != "windows"
  * @run main AttachWithStalePidFile
  */
 
@@ -45,12 +46,6 @@ import java.io.*;
 public class AttachWithStalePidFile {
   public static void main(String... args) throws Exception {
 
-    // this test is only valid on non-Windows platforms
-    if(Platform.isWindows()) {
-      System.out.println("This test is only valid on non-Windows platforms.");
-      return;
-    }
-
     // Since there might be stale pid-files owned by different
     // users on the system we may need to retry the test in case we
     // are unable to remove the existing file.