Remove a specific custom field value from an issue. Only users with push access to the repository can delete issue field values. If you don't have the proper permissions, you'll receive a `403 Forbidden` response. If the specified field does not have a value set on the issue, this operation will return a `404` error. This endpoint triggers [notifications](https://docs.github.com/github/managing-subscriptions-and-notifications-on-github/about-notifications). Creating content too quickly using this endpoint may result in secondary rate limiting. For more information, see "[Rate limits for the API](https://docs.github.com/rest/using-the-rest-api/rate-limits-for-the-rest-api#about-secondary-rate-limits)" and "[Best practices for using the REST API](https://docs.github.com/rest/guides/best-practices-for-using-the-rest-api)."