[TF2] "Duel Cancelled" notification exploit

[aarmastah]

It appears there is an exploit with the Dueling Mini-Game item that allows users to send a request to others, even when they are not in the same server, that ends up in a duel that ends instantly with a tie game. This message can be spammed repeatedly and abused.

Example 1: https://www.youtube.com/watch?v=RSlt_AY58Y4&t=1h2m49s
Example 2: https://youtu.be/aXGdQCA0iQE?t=7588

The ConVar "cl_notifications_show_ingame 0" may be able to mitigate this.

The message shown is "The duel between USER1 and USER2 has been cancelled. A Dueling Mini-Game owned by USER1 has not been consumed."