message: simplify list + operator function registration
diff: @@ -335,7 +335,7 @@ void AddFun::RegisterFunction(BuiltinFunctions &set) {
  functions.AddFunction(GetFunction(LogicalType::TIMESTAMP, LogicalType::INTERVAL));
  functions.AddFunction(GetFunction(LogicalType::INTERVAL, LogicalType::TIMESTAMP));
  // we can add lists together
  - functions.AddFunction(GetFunction(LogicalType::LIST(LogicalType::ANY), LogicalType::LIST(LogicalType::ANY)));
  + functions.AddFunction(ListConcatFun::GetFunction());
  set.AddFunction(functions);
  }
  