Revert Plek config to point to Whitehall in Carrenza Staging.
Revert Plek config to point to Whitehall in Carrenza Staging.

Reverts #9877

Testing rollback of Whitehall/Assets migration in Staging.

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