remove redundant feature declaration const_fn_transmute in lib.rs (#919)

Author: dgbo

crates/core_arch/src/lib.rs

@@ -37,8 +37,7 @@
     f16c_target_feature,
     external_doc,
     allow_internal_unstable,
-    decl_macro,
-    const_fn_transmute
+    decl_macro
 )]
 #![cfg_attr(test, feature(test, abi_vectorcall, untagged_unions))]
 #![cfg_attr(all(test, target_arch = "wasm32"), feature(wasm_simd))]