Revert "Merge pull request rust-lang#385 from workingjubilee/make-an-ass-out-of-u-and-me"

This reverts commit 6ad779c, reversing
changes made to b2e1bcb.

Author: calebzulawski

crates/core_simd/src/lib.rs

@@ -5,7 +5,6 @@
     const_maybe_uninit_as_mut_ptr,
     const_mut_refs,
     convert_float_to_int,
-    core_intrinsics,
     decl_macro,
     inline_const,
     intra_doc_pointers,

crates/core_simd/src/masks.rs

@@ -174,10 +174,7 @@ where
     #[must_use = "method returns a new mask and does not mutate the original value"]
     pub unsafe fn from_int_unchecked(value: Simd<T, N>) -> Self {
         // Safety: the caller must confirm this invariant
-        unsafe {
-            core::intrinsics::assume(<T as Sealed>::valid(value));
-            Self(mask_impl::Mask::from_int_unchecked(value))
-        }
+        unsafe { Self(mask_impl::Mask::from_int_unchecked(value)) }
     }
 
     /// Converts a vector of integers to a mask, where 0 represents `false` and -1