refactor: 移除迁移中对 think\migration\db\Column 的依赖

database/migrations/20250702075858_hello.php

@@ -1,7 +1,6 @@
 <?php
 
 use think\migration\Migrator;
-use think\migration\db\Column;
 
 class Hello extends Migrator
 {

database/migrations/20250702093625_hello2.php

@@ -1,7 +1,6 @@
 <?php
 
 use think\migration\Migrator;
-use think\migration\db\Column;
 
 class Hello2 extends Migrator
 {