rehash with channel registration disabled is unsafe

[slingamn]

Reported by eta in #ergo. loadRegisteredChannels does not check the current config value, which is probably correct: even if new channel registration is disallowed, we want to load existing registered channels. However, this case is buggy:

ergo/irc/server.go

Lines 705 to 707 in 4d9e80f

	if !oldConfig.Channels.Registration.Enabled {
	server.channels.loadRegisteredChannels(config)
	}

This will unconditionally reload the registered channels and overwrite their entries in the channel manager. I think we can actually just delete this, since we are loading the registered channels unconditionally on startup?

[slingamn]

Recommended workaround for anyone affected: set channels.registration.enabled to true, but set channels.registration.operator-only to true as well.