
### Environment

* Dubbo version: 2.7.4.1

### Steps to reproduce this issue

在dubbo正常启动的时候，会出现很多一样的警告
```
2020-03-11 22:56:34.344 [Finalizer] [WARN] com.alibaba.dubbo.config.AbstractConfig -  [DUBBO] ReferenceConfig(null) is not DESTROYED when FINALIZE, dubbo version: 2.6.4, current host: 192.168.31.245
2020-03-11 22:56:34.345 [Finalizer] [WARN] com.alibaba.dubbo.config.AbstractConfig -  [DUBBO] ReferenceConfig(null) is not DESTROYED when FINALIZE, dubbo version: 2.6.4, current host: 192.168.31.245
2020-03-11 22:56:34.345 [Finalizer] [WARN] com.alibaba.dubbo.config.AbstractConfig -  [DUBBO] ReferenceConfig(null) is not DESTROYED when FINALIZE, dubbo version: 2.6.4, current host: 192.168.31.245
```
是从下面触发了finalize()方法发出，但是现在这个里面也已经没有做任何操作了，是不是可以把finalizerGuardian去掉了？
```
 private final Object finalizerGuardian = new Object() {
        @Override
        protected void finalize() throws Throwable {
            super.finalize();

            if (!ReferenceConfig.this.destroyed) {
                logger.warn("ReferenceConfig(" + url + ") is not DESTROYED when FINALIZE");

                /* don't destroy for now
                try {
                    ReferenceConfig.this.destroy();
                } catch (Throwable t) {
                        logger.warn("Unexpected err when destroy invoker of ReferenceConfig(" + url + ") in finalize method!", t);
                }
                */
            }
        }
    };
```

* then the protocol is <b>RegistryProtocol</b></li>
     *
     * <li>when the url is dubbo://224.5.6.7:1234/org.apache.dubbo.config.api.DemoService?application=dubbo-sample, then
     * the protocol is <b>DubboProtocol</b></li>
     * <p>
     * Actually，when the {@link ExtensionLoader} init the {@link Protocol} instants,it will automatically wraps two
     * layers, and eventually will get a <b>ProtocolFilterWrapper</b> or <b>ProtocolListenerWrapper</b>
     */
    private static final Protocol REF_PROTOCOL = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
    /**
     * The {@link Cluster}'s implementation with adaptive functionality, and actually it will get a {@link Cluster}'s
     * specific implementation who is wrapped with <b>MockClusterInvoker</b>
     */
    private static final Cluster CLUSTER = ExtensionLoader.getExtensionLoader(Cluster.class).getAdaptiveExtension();
    /**
     * A {@link ProxyFactory} implementation that will generate a reference service's proxy,the JavassistProxyFactory is
     * its default implementation
     */
    private static final ProxyFactory PROXY_FACTORY = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
    /**
     * The interface proxy reference
     */
    private transient volatile T ref;
    /**
     * The invoker of the reference service
     */
    private transient volatile Invoker<?> invoker;
    /**
     * The flag whether the ReferenceConfig has been initialized
     */