Removed users are not removed after re-watching a channel

[mfbx9da4]

1. Create and watch a channel (logged in as Alice)
2. Invite Bob (as Alice)
3. Unwatch the channel (as Alice)
4. Bob rejects the invite / leaves the channel
5. Watch the channel again (as Alice)
6. Bob is still listed in state.members as invited

The issue is that this line is only additive https://github.com/GetStream/stream-chat-js/blob/master/src/channel.ts#L1356 and never removes users.

[madsroskar]

Thanks for reporting this, I've reproduced this with a test. I'll look into fixing this.