Deprecate AtLeastOne arity

[laughedelic]

There are only three types of outE/inE methods, they return

• E for arity One
• Optional<E> for arity AtMostOne
• Stream<E> for arity Any (Many)

As there is no NonEmptyStream<> in Java, let's deprecate the AtLeastOne arity.

[eparejatobes]

I like it. It's useful as documentation, at the very least.

[laughedelic]

Mmmkay.. :neutral_face: If we were using some datatype to reflect this arity, I think it would be more useful. But ok. I'm closing this.