Remove setters where possible

PluralKit.Core/Models/PKSwitch.cs

@@ -3,15 +3,8 @@
 namespace PluralKit.Core {
     public class PKSwitch
     {
-        public int Id { get; set; }
+        public int Id { get; }
         public int System { get; set; }
-        public Instant Timestamp { get; set; }
-    }
-    
-    public class PKSwitchMember
-    {
-        public int Id { get; set; }
-        public int Switch { get; set; }
-        public int Member { get; set; }
+        public Instant Timestamp { get; }
     }
 }