[libc++] Include revision numbers in the paper status lists

Several of our C++20 and C++2b papers were missing the actual revision
number that was voted in to the Standard. The revision number is quite
important because in a few cases, a paper has a revision *after* the
one that is voted into the Standard, which isn't voted into the Standard.
Hence, if we simply followed the wg21.link blindly and implemented that,
we'd end up implementing the latest revision of the paper, which might
not have been voted.

As a fly-by fix, I found out that P1664 had been withdrawn from the
straw polls and had never been voted into the Standard. This commit
removes that entry from our list.

Differential Revision: https://reviews.llvm.org/D112339