onClick event changes in 5.2.1 ?

Hello,
I was viewing the unity tutorial using the UI tools here:

and while studying it, i see that some changes were made because when i try to wrote this line as in the lesson :

yesButton.onClick.RemoveAllListeners();

with yesButton declared as Button.

if i follow the lesson, when I’m about to type in the editor “yesButton.” I don’t see any onClick events. and i got errors on the line.
What has changed?

To make it clearer, here’s a short version of the full code :

using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Events;
using System.Collections;

public class ModalPanel : MonoBehaviour {
    public Text question;
    public Image iconImage;
    public Button yesButton;
    public GameObject modalPanelObject;
    private static ModalPanel modalPanel;

    // Yes/No/Cancel: A string, a Yes event, a No event and Cancel event
    public void Choice (string question, UnityAction yesEvent, UnityAction noEvent, UnityAction cancelEvent) {
        modalPanelObject.SetActive (true);
        
        yesButton.onClick.RemoveAllListeners();  
        yesButton.onClick.AddListener (yesEvent);
        yesButton.onClick.AddListener (ClosePanel);/*HERE ARE THE ERRORS : from "onClick, everything is displayed in red, as if the method is not a part of button component*/
    }

}

Do you have (using UnityEngine.UI;) at the top of your script?