chore(builder): remove unused authorized_keys

The authorized_keys file that is actually in use is at
builder/templates/authorized_keys. This file does nothing.
fix(controller): change api logs response to 204 when no logs

The controller previously responded with a 404 (Not Found) when there
were no logs available, it now returns a 204 (No Content).

closes #990
Merge pull request #1003 from ecordell/990-fix-log-http-response

fix(controller): controller returns 204 when no logs instead of 404
Merge pull request #1000 from deis/remove-unused-keys

chore(builder): remove unused authorized_keys
chore(contrib/*): update to CoreOS 317.0.0

Double-check the IDs:
EC2: https://coreos.com/docs/running-coreos/cloud-providers/ec2/
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