Fix: Make sure Janitor can properly delete orphaned channel data

[Tohaker]

The Janitor has not been deleting historical/channel data correctly. We need to ascertain why this is happening, possibly with a new dev environment in the cloud.

• Investigate spinning up a dev environment on PRs, and tearing down after some integration tests.
• Resolve the issues found, in accordance with the new rules set out in Feature: Add "rebuild" command to reconstruct map from existing channel data carto#25