Update ssh_config
Update ssh_config

- We no longer need any of the AWS beta hosts, as far as I know
- Skyscape no longer hosts our preview environment, so make the
  comments around that more generic
- Remove reference to Lucid (10.04) because we don't run it anywhere
  now

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