Remove switch case fallthrough

[Mike Parker]

On Friday, 14 May 2021 at 08:24:46 UTC, Paulo Pinto wrote:
ines.md#es78-dont-rely-on-implicit-fallthrough-in-switch-statements
>
> Additionally, since C++17, there is the fallthrough attribute 
> to be explicit that the C behaviour is actually intended.
>
> https://en.cppreference.com/w/cpp/language/attributes/fallthrough

Man that's ugly. I like our `goto case` better.