Remove prefetchSize from channel.Qos

[Zerpet]

RabbitMQ Server does not support prefetchSize other than 0 (no limit). Setting the prefetchSize to anything other than 0 results in a channel exception "not implemented". The team does not see value in supporting a prefetch size, as most users think in terms of number of messages (as opposed to number of bytes). On top of that, if a prefetch size value is low, it would starve consumers, as no messages could be delivered.

We want to remove the prefetchSize parameter from function.