Remove the dummy function

crates/core_arch/src/mod.rs

@@ -325,15 +325,3 @@ mod nvptx;
 #[cfg(any(target_arch = "loongarch64", doc))]
 #[doc(cfg(target_arch = "loongarch64"))]
 mod loongarch64;
-
-// TODO: remove after merge of rustc #126704
-#[unstable(feature = "sha512_sm_x86", issue = "126624")]
-unsafe fn dummy() {
-    // This has to be here until PR #126704 gets merged into rustc,
-    // because otherwise rustc cannot compile because aarch64 also has
-    // a target feature named sm4, and that is stable. For `doc` env this
-    // gets compiled also in x86, but in x86 the feature sm4 is unstable
-    // So we need `feature(sha512_sm_x86)` somewhere, but if we place it without
-    // any unstable attr, rustc cannot compile stage0, because it doesn't know about
-    // this feature yet.
-}