Fixes #1923 - GCThreadLeakPreventer won't work with Java 9.

GCThreadLeakPreventer has been removed, since the issue
it was trying to fix was solved in Java 9+.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-util/src/main/java/org/eclipse/jetty/util/preventers/GCThreadLeakPreventer.java

@@ -1,59 +0,0 @@
-//
-// ========================================================================
-// Copyright (c) 1995-2020 Mort Bay Consulting Pty Ltd and others.
-//
-// This program and the accompanying materials are made available under
-// the terms of the Eclipse Public License 2.0 which is available at
-// https://www.eclipse.org/legal/epl-2.0
-//
-// This Source Code may also be made available under the following
-// Secondary Licenses when the conditions for such availability set
-// forth in the Eclipse Public License, v. 2.0 are satisfied:
-// the Apache License v2.0 which is available at
-// https://www.apache.org/licenses/LICENSE-2.0
-//
-// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
-// ========================================================================
-//
-
-package org.eclipse.jetty.util.preventers;
-
-import java.lang.reflect.Method;
-
-/**
- * GCThreadLeakPreventer
- *
- * Prevents a call to sun.misc.GC.requestLatency pinning a webapp classloader
- * by calling it with a non-webapp classloader. The problem appears to be that
- * when this method is called, a daemon thread is created which takes the
- * context classloader. A known caller of this method is the RMI impl. See
- * http://stackoverflow.com/questions/6626680/does-java-garbage-collection-log-entry-full-gc-system-mean-some-class-called
- *
- * This preventer will start the thread with the longest possible interval, although
- * subsequent calls can vary that. Recommend to only use this class if you're doing
- * RMI.
- *
- * Inspired by Tomcat JreMemoryLeakPrevention.
- */
-public class GCThreadLeakPreventer extends AbstractLeakPreventer
-{
-
-    @Override
-    public void prevent(ClassLoader loader)
-    {
-        try
-        {
-            Class<?> clazz = Class.forName("sun.misc.GC");
-            Method requestLatency = clazz.getMethod("requestLatency", new Class[]{long.class});
-            requestLatency.invoke(null, (Long)(Long.MAX_VALUE - 1));
-        }
-        catch (ClassNotFoundException e)
-        {
-            LOG.trace("IGNORED", e);
-        }
-        catch (Exception e)
-        {
-            LOG.warn("Unable to set GC latency", e);
-        }
-    }
-}