[libc++][NFC] Remove unnecessary parens in static_asserts (#95605)

These were required a long time ago due to `static_assert` not actually
being available in C++03. Now `static_assert` is simply mapped to
`_Static_assert` in C++03, making the additional parens unnecessary.

NOKEYCHECK=True
GitOrigin-RevId: 6b4b29f85900995b2a3b817548be4a534d46763b
33 files changed