Stops top menu item being triggered when opening the menu using the keyboard

Fixes https://github.com/videojs/video.js/issues/1446 

Key press handler is only active when either the MenuButton has focus or the Menu is open (allows closing the menu when a menu item is selected).
Was this removed to re-enable [the button focus listeners](https://github.com/videojs/video.js/blob/055d81dc3abc74c7a4dc88801c95cee67d2ead04/src/js/button.js#L67)?