[specialized.algorithms] `voidify` should use `\exposid`, not `\placeholdernc`

[eisenwave]

Throughout the document, we use \placeholdernc{voidify}, but this doesn't make any sense.

draft/source/algorithms.tex

Lines 13528 to 13544 in b1ff1df

	\pnum
	Some algorithms specified in \ref{specialized.algorithms}
	make use of the following exposition-only function templates:
	\begin{codeblock}
	template<class T>
	constexpr void* @\placeholdernc{voidify}@(T& obj) noexcept {
	return addressof(obj);
	}
	template<class I>
	decltype(auto) @\exposid{deref-move}@(I& it) {
	if constexpr (is_lvalue_reference_v<decltype(*it)>)
	return std::move(*it);
	else
	return *it;
	}
	\end{codeblock}

voidify is clearly declared as an exposition-only function template, so what is the \placeholdernc doing here?