[swift-evolution] Remove default case in switch-case

[Matthew Johnson]

> 1) We have had default and “case _” ever since Swift has been public.  If you look at bodies of existing swift code, they almost unanimously use “default” instead of “case _”.  This argues that default is more familiar and more widely used.  It isn’t some legacy barnacle on the side that people generally ignore.

I don’t have a strong feeling on this one way or the other, but I think it’s probably safe to say that the reason default is more familiar and widely used is because pretty much all the documentation I have seen does it that way, not because people like it better or because it is necessarily easy to understand.  If the documentation was written using "case _" I think we would see that be the familiar and widely used variation.