column privilege: REVOKE ALL(column) leaves `mysql.tables_priv` inconsistent with `mysql.columns_priv`

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
```
USE test;
CREATE USER u1;
CREATE TABLE t2 (c1 int, c2 int)
GRANT SELECT(c1), UPDATE(c2) ON t2 TO u1;
REVOKE ALL(c1) ON t2 FROM u1;
```

### 2. What did you expect to see? (Required)
```
mysql> select table_priv,column_priv from mysql.tables_priv where user='u1' and table_name='t2';
+------------+-------------+
| table_priv | column_priv |
+------------+-------------+
| | Update |
+------------+-------------+
1 row in set (0.01 sec)

```

### 3. What did you see instead (Required)
```
mysql> select table_priv,column_priv from mysql.tables_priv where user='u1' and table_name='t2';
Empty set (0.01 sec)
```
### 4. What is your TiDB version? (Required)
```
(base) ➜ bin git:(release-8.5) ./tidb-server -V
Release Version: v8.5.5-57-gf0776c1ca3
Edition: Community
Git Commit Hash: f0776c1ca3429aa20cfaad41f6e409e593680c95
Git Branch: release-8.5
UTC Build Time: 2026-03-16 10:05:43
GoVersion: go1.25.5
Race Enabled: false
Check Table Before Drop: false
Store: unistore
```