Target.AllSaved means the message will be saved in the channel.
When joining a channel you specify whether the channel's contents should be persistent or not. If they are persistent, the channel's RFC calls will be saved when the server shuts down, and loaded back up when the server is started up again.
You choose to save the server's contents, meaning everything you create / save in the channel will still be there the next time you start it up.
Either don't save it, or remove the RFC call when the player leaves. To remove a call, do it on the remaining player rather than on the player that leaves (in OnNetworkPlayerLeave). Basically the Host should clean up after the player that just left.