Removing all members from a service group does not remove the group from butterfly.

[fifthecho]

OS: Ubuntu 18.04
hab-sup versions: 0.70.0 and 0.71.0
steps to reproduce:

1. launch a new service in a group (hab svc run core/consul --group foo) in a supervisor connected to a bastion ring
2. unload that service
3. see that the service group and information about the service is still contained within the bastion ring.

expected behavior:
either being able to manually delete a service group (or group member) via the bastion ring or having the service or service member leave the group when the service is unloaded. If no members exist, delete the service.

https://forums.habitat.sh/t/service-unloaded-node-persists/956/3

[fifthecho]

Largely a duplicate of #5325. Closing.