Remove "costs" & "other notes" fields from stubs.

These will only be useful when we have Transaction Explorer data
about costs on the dashboards. At the moment, there's no data
about costs being shown - so these are superfluous.

Remove them from Stagecraft stubs.
Merge pull request #316 from alphagov/bugfix/remove-unused-fields-from-config

Remove "costs" & "other notes" fields from stubs.