why the "rocketmq_group_count" can get the consumer group that has been deleted

[hahait]

Describe the bug I have many consumer groups has been deleted from namesrv，then exec shell command mqadmin consumerProgress -n <namesrv ip>:9876 ，can not get those consumer groups， but the metric rocketmq_group_count can get； The metric rocketmq_group_diff can not get those consumer groups that has been deleted，Is the right;

To Reproduce Steps to reproduce the behavior:

1. mqadmin deleteSubGroup -g <group name> -n <namesrv ip>:9876 -c DefaultCluster，delete several groups;
2. mqadmin consumerProgress -n <namesrv ip>:9876, Confirm the result of the deletion；
3. Get the value of the metric rocketmq_group_count, Check that those deleted groups still exist ;

Expected behavior rocketmq_group_count cannot get the deleted consumer groups;

Desktop (please complete the following information):

• OS: debian 10
• Browser: chrome
• Version: master

[francisoliverlee]

all group comes from code bellow, you can check it

https://github.com/apache/rocketmq/blob/a20f31bb3de242756542c552d7212a7a40000ba4/broker/src/main/java/org/apache/rocketmq/broker/processor/AdminBrokerProcessor.java#L199

[maixiaohai]

https://github.com/apache/rocketmq/issues/3181

[humkum]

I'd like to follow this issue.

[maixiaohai]

I'd like to follow this issue.

welcome submit a pr to fix it