[libc++][NFC] Update LWG3477(Simplify constraints for `semiregular-box`) status (#85399)

Since we implemented `copyable-box` in
(https://reviews.llvm.org/D102135,
https://github.com/llvm/llvm-project/commit/6829db727e9e67dfdb70dd0846ffd4e48e00a98d

),
this issue got addressed.

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Signed-off-by: yronglin <yronglin777@gmail.com>