Private channel names are sent out publicly through websocket when being removed

[Kelton555]

Private channel names get sent out publicly on the websocket when being removed; i.e. when the last user disconnects or joins a different channel. Disconnecting is of particular importance as people will rejoin the same private channel when they next reconnect, potentially leading to the leakage of private channels that are still in use.

The cause is the hard-coded 'false' here: https://github.com/0x0ade/CelesteNet/blob/405a7e5e4d78727cd35ee679a730400b0a46667a/CelesteNet.Server.FrontendModule/Frontend.cs#L188