[libc++] Revert temporary attempt to implement LWG 4110 (#95263)

When I filed LWG4110 after the discussion in #93071, I thought it was
going to be a straightforward fix. It turns out that it isn't, so we
should stay in the state where libc++ is Standards conforming even if
that state leads to some reasonable code being rejected by the library.
Once WG21 figures out what to do with this issue and votes on it, we'll
implement it through our normal means.

This reverts f638f7b6a7c2 and 16f2aa1a2ddf.

GitOrigin-RevId: a66e2a1988cb14ec2feadfbc3dd1ff4bd77f4be9
6 files changed