Q: How to set AirPort Express as receiver only?

Your question is quite unclear to me. You don't want the Express to broadcast anything, but it should provide internet connection for the tv? That is not possible: internet connections are always a two-way affair. The best solution probably would be to use the Express in client mode. Follow these instructions: AirPort Express: How to join an existing Wi-Fi network in client mode - Apple Support

Go to system preferences > security & privacy > open the padlock by entering user name & password > select firewall > click on firewall options >enable stealth mode & close the pad lock .

As stealth mode cloaks you from initiating traffic , on enabling stealth mode firewall watches the echo request come in,& instead of denying it , it simply tells your system to ignore the packet .

The machine on the other end not only doesn't get any data as if their packet was just lost in space .

Stealth mode makes your mac invisible to ping attempts by hackers trying to locate your machine on a network and also  ip address is hidden , its just like a mask on network & acts like a ghost mode / just like tin foil hat , if any one pings through network they are reflected so security network performance are improved with this configuration .

Sometimes incoming packets are more than sent packets means internet traffic is diverted to your network , but due to stealth mode that is enabled machine rejects the packets .

So, by enabling stealth mode machine will receive signals but will not broadcast anything .

It sounds like you have the AirPort Extreme acting as both a normal WiFi base-station for client devices and also as half of a wireless link to another base-station i.e. the Express. It also sounds like you want the AirPort Express to act as its half of the wireless link but not to accept wireless client devices and to instead just be connected via Ethernet to your TV set.

If you think about this the wireless link between the AirPort Extreme and Express will require traffic to go in both directions as the TV will send commands via that wireless link to the AirPort Extreme and hence to the Internet, and in return results - presumably a streamed program will go back via the wireless link to the TV.

What you can do is set the AirPort Express half of the wireless setup to not accept client devices and to only operate as a wireless link to the Extreme. I only have two Extreme units and older models so it maybe different but on mine I get an option under wireless settings labelled 'Allow wireless clients' and this would be what you want unticked on the Express unit.