You can’t remotely wipe or reset Apple TV like you can iPhone, iPad or a Mac. However, you can remove the device from your Apple ID account. The new owner will most likely reset the device in order to login with their own Apple ID, otherwise they will be nagged to enter your Apple ID password all the time. I wouldn’t worry about your purchased content.
To prepare your Apple TV for a new owner, use these steps reset it to factory settings and remove it from your associated devices.
support.apple.com