销毁 clipboard 前是否应该取消订阅？

[Zclhlmgqzc]

https://github.com/Inndy/vue-clipboard2/blob/8a542c558c6857212d06f6fc1929384a5b5104cc/vue-clipboard.js#L72

+ const clipboard = el._vClipboard
+ clipboard.off('success')
+ clipboard.off('error')
+ clipboard.destroy()
- el._vClipboard.destroy()
+ el._vClipboard = null
delete el._vClipboard