Can you explain why you can't just not give the TV your Wi-Fi password?
Or are we worried about the case when the TV did have Wi-Fi (due to it being mandatory for some initial setup, say), but we don't trust that "Forget Network" and "Wi-Fi off" are actually honored?
Suppose the device surreptitiously reconnects to Wi-Fi in spite of being told to forget it. You may be able to block it in your router and failing that, change the access point password.
No?
But if the TV manufacturer is smart in their spying game, they could also be probing for any public SSIDs to connect to when no local internet access is setup.
Doesn't exactly sound like a thing to be that concerned about if you never plug in your TV. If you buy a TV right now and never plug it in, how would it know about any future deal with Xfinity to connect to its open networks? And if it had a feature to connect to random open Wi-Fi networks right now, that wouldn't be hard to prove. My LG has never shown up in my Wi-Fi client list despite my open guest Wi-Fi. You can even test it by naming your guest network "Xfinity WiFi".
Taking apart your TV and pulling out the wireless radio sounds like absolute overkill to me. Feel free to do it if it makes you feel better. It will definitely not allow it to send data (over Wi-Fi) under any circumstance. I'm just not convinced that the alternative is that much riskier.
I assume at some point, appliance manufacturers will start "partnering" with things that actually need WiFi for exfiltration purposes. Phones would be a good place to start.
That way, we'd need to either Faraday cage our friends' phones, not invite them over, or send marketing pervs video feed of our moldy pickles.