Removes the first occurrence of the specified element from this list, if it is present (optional operation). If this list does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).
刪除第一個出現的相同對象，判斷時，需要使用equals方法，如果是自己創建的對象，需要重寫類的hashCode和equals方法