Remove static methods that arent overridable

lib/structs/JsonSerializable.dart

@@ -8,14 +8,4 @@ abstract class IJsonSerializable {
 
   /// Returns a Json Object
   Map<String,dynamic> toJson();
-
-  /// Decodes json and returns the instance
-  static IJsonSerializable fromJson(String js) {
-    throw UnimplementedError();
-  }
-
-  /// Decodes json object
-  static IJsonSerializable decode(Map<String,dynamic> js) {
-    throw UnimplementedError();
-  }
 }