[Bug libstdc++/86537] std::less specialization for std::shared_ptr

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86537

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The changes from lwg 1262 were implemented by r171293 but we never got rid of
the partial specialization of std::less.