Superagen 'del' change from status 200 to 204

[barberdt]

For each of the instances of superagent delete requests, change the expected success status from 200 to 204.

[c4milo]

I did a quick review and the only place where I need to make the change is in https://github.com/buglabs/bugswarm-api/blob/master/nodejs/configuration/lib/swarm.js#L378