(lib/sleep_until) allow unused code for Instant::into_inner

Author: dvdsk

library/std/src/time.rs

@@ -404,6 +404,8 @@ impl Instant {
         self.0.checked_sub_duration(&duration).map(Instant)
     }
 
+    // used by platform specific sleep_until implementations, no every platform has one
+    #[allow(unused)]
     pub(crate) fn into_inner(self) -> time::Instant {
         self.0
     }