`<xutility>`: What's the intent of the pseudo-documentation?

[frederick-vs-ja]

The class template _Is_checked_helper has been left unused since the initial commit on Github.

STL/stl/inc/xutility

Lines 1305 to 1306 in 25dc2b7

	template <class, class = void>
	struct _Is_checked_helper {}; // default definition, no longer used, retained due to pseudo-documentation

It's unclear what the "pseudo-documentation" is. Perhaps we should either improve the comment or entirely remove _Is_checked_helper.

[StephanTLavavej]

We talked about this at the weekly maintainer meeting. We believe that _Is_checked_helper should be outright removed - it's been a long time since we overhauled the checking machinery and provided a better, more-documented way for users to opt in. We doubt there was significant uptake of the old mechanism, and it's undesirable to continue providing _Is_checked_helper which could confuse users into thinking that it actually accomplishes something. Let's rip it out and see if any codebases notice. (If we they do, we could explore other options - reporting/fixing issues upstream, adding it back with an escape hatch, etc.).