Figure out if ticket based ack is actually usefull

[arthurprs]

Amazon SQS has the concept of a receipt that's different from the Message ID, its used to delete (ack) the message afterwards. Also, if a messages timeout a new receipt is generated and the old one can't be used anymore.

I tried to mimic the concept here with a different name (ticket) but I'm unsure if it's actually useful. I use/used SQS extensively and I never found this actually useful.

Removing this features allow Floki to store a little bit less inflight metadata in memory.

I appreciate any inputs on this.