Update Domain.cs to remove orgs api entry (#752)

Author: AsabuHere

src/Twilio/Rest/Domain.cs

@@ -31,7 +31,6 @@ public static implicit operator Domain(string value)
         public static readonly Domain Events = new Domain("events");
         public static readonly Domain FlexApi = new Domain("flex-api");
         public static readonly Domain FrontlineApi = new Domain("frontline-api");
-        public static readonly Domain PreviewIam = new Domain("preview-iam");
         public static readonly Domain Insights = new Domain("insights");
         public static readonly Domain Intelligence = new Domain("intelligence");
         public static readonly Domain IpMessaging = new Domain("ip-messaging");
@@ -60,4 +59,4 @@ public static implicit operator Domain(string value)
         public static readonly Domain Wireless = new Domain("wireless");
     }
 
-}
+}