Revamp Lotka-Volterra ODE model with new syntax

[jonah]

We have an issue now with most of the case studies not working with 2.33+:

How to handle case studies on website with old syntax

@SGB Many (most?) case studies hosted on the Stan website will now error with 2.33+ because they use the old array syntax. How should we address this? Ask devs and/or community members to volunteer to update them all? Ask authors to update them? Add a disclaimer at the top of the case studies page that some use old syntax? Something else? It would be good to address this soon since 2.33 is now released.