It is expected, as the goal is to get rid of the “hide relay” and “delete relay” distinction. When you delete a relay, it is actually deleted after determining that it does not receive any more messages (for 90 days).
It seems that while dialing an audio call, TURN server will be get from all relays.
I added a relay other than my own server, and I wanted to delete it so that the TURN server of my own relay come into use.
But it seems now that there is no way to delete the unwanted relay immediately. And its TURN server is used while calling. So it seems that I have no way to use my own server TURN relay, right?
Yes, currently TURN servers are basically picked at random. See Calls: use all relays' TURN servers, not just one.
If you want to circumvent this, create a fresh profile from the relay’s invite link.