Remove deprecated Certificate contact_id field (#236)

The `contact_id` field in the Certificate schema was deprecated on
2022-05-17 and is no longer required for certificate operations. Remove
`ContactId` from the `Certificate` struct and from
`LetsencryptCertificateAttributes`.

This is a breaking change.

Related to dnsimple/dnsimple-developer#987

Author: weppos

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 This project uses [Semantic Versioning 2.0.0](http://semver.org/), the format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## main
+
+### Removed
+
+- **BREAKING**: Removed the deprecated `ContactId` field from the `Certificate` struct and from `LetsencryptCertificateAttributes`. The field was deprecated on 2022-05-17 and is no longer required for certificate operations.
+
 ## 1.3.0 - 2026-04-15
 
 ### Added

src/dnsimple/Services/Certificates.cs

@@ -187,8 +187,6 @@ public struct CertificateRenewal
     [JsonObject(NamingStrategyType = typeof(SnakeCaseNamingStrategy))]
     public struct LetsencryptCertificateAttributes
     {
-        [ObsoleteAttribute("ContactId is deprecated and its value is ignored and will be removed in the next major version.")]
-        public long? ContactId { get; set; }
         public bool AutoRenew { get; set; }
         public string Name { get; set; }
         public List<string> AlternateNames { get; set; }
@@ -203,8 +201,6 @@ public struct Certificate
     {
         public long Id { get; set; }
         public long DomainId { get; set; }
-        [ObsoleteAttribute("ContactId is deprecated and its value is ignored and will be removed in the next major version.")]
-        public long ContactId { get; set; }
         public string CommonName { get; set; }
         public long Years { get; set; }
         public string Csr { get; set; }