Remove validUntil from API response

## Background
In December during engagement with platforms around the regulatory amendments for exemptions and renewal workflows, some platforms requested that we provide the expiry date for a given registration so that they could support their customers with the renewal process. Upon review with Legal, it was determined that the expiry date constitutes PII and its disclosure is not covered under the legislation (STRAA) or appropriate use under existing privacy laws, including the Personal Information Protection Act (PIPA) and the Freedom of Information and Protection of Privacy Act (FOIPPA).

Upon further investigation it was determined that the expiry date was already being provided in the response to the ValidatePermit request. As a result, Legal has recommended that we remove this data from the response.

## User stories / Requirements

- In order to prevent exposure of personal information, the “validUntil” field is no longer shared as part of the ValidatePermit response
- Ensure that integrated platforms are not negatively impacted by removal of the validUntil data from the response
- Documentation is updated to reflect the updated specification / expected behavior of the API