[PATCH] Simplify _Node_insert_return to avoid including <tuple>

[Jonathan Wakely]

On 02/11/17 18:00 -0400, Tim Song wrote:
>Um, why are those member get's there at all (and with an index mapping
>that doesn't agree with the member order)? [container.insert.return]
>says that "It has no base classes or members other than those
>specified."

Because I forgot to implement https://wg21.link/p0508r0 which changed
the spec, including the order of the members.

I'll do that shortly, thanks.