Remove autoscaling group

[raxod502]

https://riju.statuspage.io/incidents/3j942jd9q374 was caused basically because autoscaling groups are confusing. I still don't fully understand what happened. But it occurred to me that the autoscaling group itself isn't really doing anything here, after all we're not actually doing any autoscaling.

Instead, we can just define the target group, and add/remove instances to the target group directly. That should cover everything we need. We can also write a script to handle the common case of rolling the instances with a new AMI.

[raxod502]

Done in the above-linked commit. See also https://riju.statuspage.io/incidents/s6dr9yjvqxy2.