refactor: remove obsolete Order.ProcessingMethod property

BREAKING CHANGE: anyone relying on this property will need to find an alternative.

ShopifySharp/Entities/Order.cs

@@ -230,13 +230,6 @@ public class Order : ShopifyObject
     [JsonProperty("processed_at")]
     public DateTimeOffset? ProcessedAt { get; set; }
 
-    /// <summary>
-    /// The type of payment processing method. Known values are 'checkout', 'direct', 'manual', 'offsite', 'express', 'free' and 'none'.
-    /// </summary>
-    [JsonProperty("processing_method")]
-    [Obsolete("Deprecated in version 2023-04. https://shopify.dev/docs/api/release-notes/2023-04#payment-properties-on-the-order-resource-have-been-removed")]
-    public string ProcessingMethod { get; set; }
-
     /// <summary>
     /// The website that the customer clicked on to come to the shop.
     /// </summary>
@@ -515,4 +508,4 @@ public class Order : ShopifyObject
 
     [JsonProperty("company")]
     public OrderCompany Company { get; set; }
-}
+}