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);
        }
    }
~~~
private Set<ConfigurationListener> listeners = new CopyOnWriteArraySet<>();
        /**
         * cache data to store old value
         */
        private Map<String, String> cacheData = new ConcurrentHashMap<>();
        @Override
        public Executor getExecutor() {
            return null;
        }
        /**
         * receive
         *
         * @param dataId     data ID
         * @param group      group
         * @param configInfo content
         */
        @Override
        public void innerReceive(String dataId, String group, String configInfo) {
            String oldValue = cacheData.get(dataId);
            ConfigChangedEvent event = new ConfigChangedEvent(dataId, group, configInfo, getChangeType(configInfo, oldValue));
            if (configInfo == null) {