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);
        }
    }
~~~
import org.apache.dubbo.common.config.configcenter.ConfigurationListener;
import org.apache.dubbo.common.utils.JsonUtils;
import org.apache.dubbo.common.utils.MD5Utils;
import org.apache.dubbo.common.utils.StringUtils;
import org.apache.dubbo.metadata.MappingChangedEvent;
import org.apache.dubbo.metadata.MappingListener;
import org.apache.dubbo.metadata.MetadataInfo;
import org.apache.dubbo.metadata.ServiceNameMapping;
import org.apache.dubbo.metadata.report.identifier.BaseMetadataIdentifier;
import org.apache.dubbo.metadata.report.identifier.KeyTypeEnum;
import org.apache.dubbo.metadata.report.identifier.MetadataIdentifier;
import org.apache.dubbo.metadata.report.identifier.ServiceMetadataIdentifier;
import org.apache.dubbo.metadata.report.identifier.SubscriberMetadataIdentifier;
import org.apache.dubbo.metadata.report.support.AbstractMetadataReport;
import com.alibaba.nacos.api.NacosFactory;
import com.alibaba.nacos.api.PropertyKeyConst;
import com.alibaba.nacos.api.config.listener.AbstractSharedListener;
import com.alibaba.nacos.api.exception.NacosException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.concurrent.Executor;
import static com.alibaba.nacos.api.PropertyKeyConst.SERVER_ADDR;