Prevent error after kick user
Prevent error after kick user

This simple change helps to prevent `'The conference is has been already left'` error after kick. 
`Conference.leave` will detach chatRoom instance itself.
jitsi/lib-jitsi-meet,jitsi/lib-jitsi-meet,damencho/lib-jitsi-meet,jiyeyuran/lib-jitsi-meet