perf[clipboard.js]: remove redundant code (PanJiaChen#2307)

Author: mayunhai

src/utils/clipboard.js

@@ -22,14 +22,10 @@ export default function handleClipboard(text, event) {
   })
   clipboard.on('success', () => {
     clipboardSuccess()
-    clipboard.off('error')
-    clipboard.off('success')
     clipboard.destroy()
   })
   clipboard.on('error', () => {
     clipboardError()
-    clipboard.off('error')
-    clipboard.off('success')
     clipboard.destroy()
   })
   clipboard.onClick(event)