Generate column shouldn't store schema name and table name

[Defined2014]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

use test;
create table t(a int);
alter table t add column b int as ((lower(test.t.a)));
rename table t to t1;
insert into t1(a) values (1);

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

insert success

3. What did you see instead (Required)

mysql> insert into t1(a) values (1);
ERROR 1054 (42S22): Unknown column 'test.t.a' in 'expression'

4. What is your TiDB version? (Required)

master