stats should not count expired vertex\edge data

[nebula-bots]

Your Environments (required)

How To Reproduce(required)

• Background

Given create a space with following options:
            | partition_num  | 9                |
            | replica_factor | 1                |
            | vid_type       | FIXED_STRING(30) |
            | charset        | utf8             |
            | collate        | utf8_bin         |
        And executing query:
            """
            CREATE TAG player(name string, age int, update_time timestamp DEFAULT now())TTL_DURATION= 10, TTL_COL = "update_time";
            CREATE TAG team(name string);
            CREATE EDGE follow(start_time timestamp DEFAULT now(), degree int)TTL_DURATION= 10, TTL_COL = "start_time";;
            CREATE EDGE serve(start_year int, end_year int);
            CREATE TAG INDEX player_index_1 ON player(name(10),age);
            CREATE EDGE INDEX follow_index_1 ON follow(start_time);
            """
        And retry executing query:
            """
            INSERT VERTEX player(name, age) VALUES "player100":("Tim Duncan", 42);
            INSERT VERTEX player(name, age) VALUES "player101":("Tony Parker", 36);
            INSERT VERTEX player(name, age) VALUES "player102":("LaMarcus Aldridge", 33);
            INSERT VERTEX team(name) VALUES "team203":("Trail Blazers"), "team204":("Spurs");
            INSERT EDGE follow(degree) VALUES "player101" -> "player100":(95);
            INSERT EDGE follow(degree) VALUES "player101" -> "player102":(90);
            INSERT EDGE follow(degree) VALUES "player102" -> "player100":(75);
            INSERT EDGE serve(start_year, end_year) VALUES "player101" -> "team204":(1999, 2018),"player102" -> "team203":(2006,  2015);
            """

• View stats data before expiration

submit job stats;
show stats;

• When sleep 11 s, View stats data after expiration

submit job stats;
show stats;

Expected behavior
stats should not count expired vertex\edge data

[Sophie-Xie]

Discuss it offline with fangyang, jingchun, siwang : If we fix it, we need to make a lot of changes. And it still won't be statistically accurate, so we will not fix it.