[Bug c++/91383] C++17 should remove some library feature deprecated in C++14

[ufospoke at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91383

--- Comment #2 from Frédéric Bron <ufospoke at gmail dot com> ---
I agree that in C++14, they should be marked deprecated.
But the features have been removed in C++17. They are not deprecated anymore,
so in my opinion, they should not be available with -std=c++17.