Remove special-case for `simd_shuffle` intrinsics in promotion

[ecstatic-morse]

#69280 tried to normalize promotion of arguments that must be const by requiring #[rustc_args_required_const] everywhere. Currently, intrinsics beginning with the string "simd_shuffle" automatically get their third argument promoted. However, this broke the latest release of the packed_simd crate, which does not define the intrinsics with the requisite attribute (see #69313).

Although this is allowed breakage (you can't define intrinsics without the nightly-only platform_intrinsics feature), I reverted #69280 for now, since it's just a small cleanup and isn't blocking anything. I opened rust-lang/packed_simd#278 to fix packed_simd. Once a version of that crate is released with the fix, we should reapply #69280.

[workingjubilee]

@rustbot modify labels: +A-simd
I guess? 🤷

[mati865]

Packed_simd seems unmantained these days, I think it had enough time adjust.