deleted system table still can be get from information_schema

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table in mysql db
drop table
check with "select * from information_schema"

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

can't find this table in information_schema

3. What did you see instead (Required)

still exist

4. What is your TiDB version? (Required)

master

[seiya-annie]