[libcxx] removes unnecessary traits from `has_unique_object_representations` (#69241)

`remove_cv_t` and `remove_all_extents_t` are taken care of by the
built-in trait, so we don't need to use them directly.

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Co-authored-by: Louis Dionne <ldionne.2@gmail.com>
NOKEYCHECK=True
GitOrigin-RevId: 8b8ad75cc94aad88c505bdca71c903774f9e75c7
2 files changed