Remove switch case fallthrough

[Steven Schveighoffer]

On 5/13/21 9:28 AM, rempas wrote:
> Yeah yeah I know I know, Code that looks like C should have the same 
> behavior to C. I've asked about that and I got the same answer. But come 
> one! We can make an exception on this one! We don't need that in D as we 
> can add more cases.

It's already deprecated, since 2.072. It's also been a warning since 
2.054. I'm not sure if this is intended to be removed or not, but 
removing it today would put it at a 4.5 year deprecation period, and 10 
years since it's been a warning.

> 
> I really love the work the contributors do with D but IMO is things like 
> that who really stop D from REALLY going forward in the next level. 
> Doing things just for doing them NEVER helped anyone!

Nobody thinks case fallthrough is good, this is why it's a warning and 
deprecated.

-Steve