Removing the staging over-ride
Removing the staging over-ride

While migrating mapit we wanted staging to not have an entry in `/etc/hosts`.
These are seeded through the app_hostnames var. Now that mapit has migrated we
no longer need a specific config for staging and can rely on the common.yaml.

solo: da39a3ee5e6b4b0d3255bfef95601890afd80709@jstandring-gds

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet