TiFlash with S3 remote_gc can't work as expected

[lilinghai]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

insert some table and select count(*) using tiflash. deploy tiflash with s3 using minio
tiflash wn config

 remote_gc_interval_seconds = 60
 remote_gc_method = 2

2. What did you expect to see? (Required)

s3 can gc as expeted

3. What did you see instead (Required)

s3 data size about 3.3T , while tikv all store size 800G

4. What is your TiFlash version? (Required)

master