#346 lyon2024: internal code needs clean up

[Piotr Majdak]

lyon2024 uses vargout to determine what to calculate, but this is a complicated way of handling model parameters. More nice is the way other models such as dau1997, verhulst2018, or osses2021 do. When this is resolved, the local function can be removed because it is now called multiple times only because of that output assignment...