[Bug Report] cascader-node.vue binding events

### Element UI version
2.14.1

### OS/Browsers version
window 10

### Vue version
3.0.4

### Reproduction Link
https://codepen.io/huangxiaomin/pen/RwGojxW

### Steps to reproduce
cascader-node组件渲染时,下面代码会有重复行为
if (expandTrigger === 'click') {
events.on.click = this.handleExpand;
} else {
events.on.mouseenter = e => {
this.handleExpand();
this.$emit('expand', e);
};
events.on.focus = e => {
this.handleExpand();
this.$emit('expand', e);
};
}
if (isLeaf && !isDisabled && !checkStrictly && !multiple) {
events.on.click = this.handleCheckChange;
}

### What is Expected?
其实只需要执行一次就可以了

### What is actually happening?
执行两次this.panel.handleExpand
模式为click时，如果时叶子节点条件为isLeaf && !isDisabled && !checkStrictly && !multiple时这边也会执行，和下面的判断重复了，重复执行了this.panel.handleExpand