Remove const_eval_select hack

Author: oli-obk

core/src/intrinsics/mod.rs

@@ -2279,7 +2279,7 @@ pub const fn const_eval_select<ARG: Tuple, F, G, RET>(
 ) -> RET
 where
     G: FnOnce<ARG, Output = RET>,
-    F: FnOnce<ARG, Output = RET>;
+    F: const FnOnce<ARG, Output = RET>;
 
 /// A macro to make it easier to invoke const_eval_select. Use as follows:
 /// ```rust,ignore (just a macro example)