[libcxx-commits] [libcxx] [libc++][NFC] Simplify pair a bit (PR #96165)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne approved this pull request.

LGTM if CI passes, but I am pretty sure the code was written that way because this was upsetting compilers at some point. The condition inside `explicit` is technically not dependent as written, and I think this was causing problems.

Again, if CI happy, I am happy.

https://github.com/llvm/llvm-project/pull/96165