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);
        }
    }
~~~
@Override
    protected List<String> doGetExportedURLs(ServiceMetadataIdentifier metadataIdentifier) {
        String content = getConfig(metadataIdentifier);
        if (StringUtils.isEmpty(content)) {
            return Collections.emptyList();
        }
        return new ArrayList<String>(Arrays.asList(URL.decode(content)));
    }
    @Override
    protected void doSaveSubscriberData(SubscriberMetadataIdentifier subscriberMetadataIdentifier, String urlListStr) {
        storeMetadata(subscriberMetadataIdentifier, urlListStr);
    }
    @Override
    protected String doGetSubscribedURLs(SubscriberMetadataIdentifier subscriberMetadataIdentifier) {
        return getConfig(subscriberMetadataIdentifier);
    }
    @Override
    public String getServiceDefinition(MetadataIdentifier metadataIdentifier) {
        return getConfig(metadataIdentifier);
    }
    @Override
    public boolean registerServiceAppMapping(String key, String group, String content, Object ticket) {
        try {
            if (!(ticket instanceof String)) {
                throw new IllegalArgumentException("nacos publishConfigCas requires string type ticket");
            }
            return configService.publishConfigCas(key, group, content, (String) ticket);
        } catch (NacosException e) {
            logger.warn("nacos publishConfigCas failed.", e);
            return false;