1. 继承 List<T>
2. 新建方法：
   RemoveMaxItem()
   RemoveMinItem()
3. 实现方法：
public void RemoveMaxItems()
{
    this.RemoveAll(e => e.Equals(this.Max()));
}
public void RemoveMinItems()
{
    this.RemoveAll(e => e.Equals(this.Min()));
}
4. 测试：
MyList<int> list = new MyList<int> { 11, 2, 2, 2, 5, 6, 7, 8, 9, 10, 11 };
Console.WriteLine(String.Join<int>(" - ", list));
list.RemoveMaxItems();
Console.WriteLine(String.Join<int>(" - ", list));
list.RemoveMinItems();
Console.WriteLine(String.Join<int>(" - ", list));