refactor(polyfills): 移除 php::Var 类型常量

- 删除了 type_any 常量定义
- 清理了相关类型声明代码

src/polyfills.php

@@ -11,7 +11,6 @@ class native_types
     public const type_int = 'int';
     public const type_float = 'float';
     public const type_bool = 'bool';
-    public const type_any = 'php::Var';
 }
 
 class std