swift234

Set: Rename removeFirst -> removeAny and first -> any

Rename in Set<T>:

func removeFirst() -> T
to
func removeAny() -> T?

var first: T?
to
var any: T?

- FWIW, `any` more closesly matches NSSet's `anyObject()` and constructs
  in other languages, so `first` seems to be a bit of a surprise.
- `first` implies an ordering of some kind, iterating over `Set` as a
  `SequenceType` does have a somewhat reliably "first" element, but it
  also has a linguistic tension with the fact that Set<T> is
  semantically unordered.
- `first` may be further confused if there ever is an OrderedSet<T>,
  which ought to be the first element in its semantic ordering.

Swift SVN r23696