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);
        }
    }
~~~
throw new IllegalStateException(e.getMessage(), e);
        }
    }
    @Override
    public MetadataInfo getAppMetadata(SubscriberMetadataIdentifier identifier, Map<String, String> instanceMetadata) {
        try {
            String content = configService.getConfig(identifier.getApplication(), identifier.getRevision(), 3000L);
            return JsonUtils.getJson().toJavaObject(content, MetadataInfo.class);
        } catch (NacosException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
    }
    @Override
    protected void doStoreProviderMetadata(MetadataIdentifier providerMetadataIdentifier, String serviceDefinitions) {
        this.storeMetadata(providerMetadataIdentifier, serviceDefinitions);
    }
    @Override
    protected void doStoreConsumerMetadata(MetadataIdentifier consumerMetadataIdentifier, String value) {
        if (getUrl().getParameter(REPORT_CONSUMER_URL_KEY, false)) {
            this.storeMetadata(consumerMetadataIdentifier, value);
        }
    }
    @Override
    protected void doSaveMetadata(ServiceMetadataIdentifier serviceMetadataIdentifier, URL url) {
        storeMetadata(serviceMetadataIdentifier, URL.encode(url.toFullString()));
    }
    @Override
    protected void doRemoveMetadata(ServiceMetadataIdentifier serviceMetadataIdentifier) {
        deleteMetadata(serviceMetadataIdentifier);
    }