`absl::int128` and `absl::uint128` are not `std::is_integral`. There is an internal `IsIntegral` type trait we could use, but it actually makes more sense to remove the `static_assert` altogether. Any compile-time validation should be done in `absl::Uniform` itself, and duplicating that logic here just increases the chance of divergence.

PiperOrigin-RevId: 635971431
Change-Id: I9177ae64c86ee1abe6571e0b29aba1844553c972