问题描述：NacosMetadataReport#getServiceAppMapping 方法将监听器存入casListenerMap中，key是使用 DEFAULT_MAPPING_GROUP
作为group构建；但是 NacosMetadataReport#removeServiceAppMappingListener方法中，移除监听器时使用group不是 DEFAULT_MAPPING_GROUP，从而导致无法正常移除监听器

~~~
@Override
    public Set<String> getServiceAppMapping(String serviceKey, MappingListener listener, URL url) {
        String group = DEFAULT_MAPPING_GROUP;

        if (null == casListenerMap.get(buildListenerKey(serviceKey, group))) {
            addCasServiceMappingListener(serviceKey, group, listener);
        }
        String content = getConfig(serviceKey, group);
        return ServiceNameMapping.getAppNames(content);
    }

    @Override
    public void removeServiceAppMappingListener(String serviceKey, MappingListener listener) {
        MappingDataListener mappingDataListener = casListenerMap.get(buildListenerKey(serviceKey, group));
        if (null != mappingDataListener) {
            removeCasServiceMappingListener(serviceKey, group, listener);
        }
    }
~~~
try {
            configService.addListener(key, group, nacosConfigListener);
        } catch (NacosException e) {
            logger.error(e.getMessage());
        }
    }
    public void removeListener(String key, String group, ConfigurationListener listener) {
        String listenerKey = buildListenerKey(key, group);
        NacosConfigListener nacosConfigListener = watchListenerMap.get(listenerKey);
        try {
            if (nacosConfigListener != null) {
                nacosConfigListener.removeListener(listener);
                if (nacosConfigListener.isEmpty()) {
                    configService.removeListener(key, group, nacosConfigListener);
                    watchListenerMap.remove(listenerKey);
                }
            }
        } catch (NacosException e) {
            logger.error(e.getMessage());
        }
    }
    private NacosConfigListener createTargetListener(String key, String group) {
        NacosConfigListener configListener = new NacosConfigListener();
        configListener.fillContext(key, group);
        return configListener;
    }
    private String buildListenerKey(String key, String group) {
        return key + HYPHEN_CHAR + group;
    }
    private void storeMetadata(BaseMetadataIdentifier identifier, String value) {