Keep AirPlay toolbar icon permanently visible or hidden
You can disable the icon in the menu bar by ⌘-dragging it off the menu bar, which unchecks the option in System Preferences → Displays entitled "Show mirroring options in the menu bar when available".

Should you wish to use the menu bar item, you can check this box again, or just use the AirPlay Display dropdown in System Preferences → Displays to connect to an AirPlay device.