def remove_user(nick)
      @mutex.synchronize do
        channels = Set.new

        @channels.each do |channel|
          if channel.remove_user(nick)
            channels << channel
          end
        end

        channels
      end
    end
def remove_user(nick)
      @mutex.synchronize do
        channels = Set.new

        @channels.each do |channel|
          if channel.remove_user(nick)
            channels << channel
          end
        end

        channels
      end
    end
Removes a User from all Channels from the ChannelList.
 Returning a Set of Channels in which the User was.