SE-0232: Remove Some Customization Points from the Standard Library's Collection Hierarchy

[Nevin]

@Ben_Cohen

drop* , prefix , suffix , and shudder split are a different matter. They are customization points because they return an associated type .

I see. What about prefix(upTo:), prefix(through:) and suffix(from:) on Collection? Those have implementations in terms of subscript(bounds:), and I can’t imagine doing anything else.