libstdc++: Implement LWG 3404 for C++20 subrange [PR 100044]
These deduction guides became useless with LWG 3282 (implemented in
commit r10-6741) and so were removed by LWG 3404.
libstdc++-v3/ChangeLog:
PR libstdc++/100044
* include/bits/ranges_util.h (__detail::__iterator_sentinel_pair):
Remove helper concept.
(subrange(_Pr), subrange(Pr, __make_unsigned_like<...>)): Remove
deduction guides, as per LWG 3404.
* testsuite/std/ranges/subrange/lwg3282_neg.cc: Check that class
template argument deduction fails.