Expose time::deplay_queue::Expired::deadline (#2300)

* Expose time::deplay_queue::Expired::deadline

* Return by value

tokio/src/time/delay_queue.rs

@@ -879,4 +879,9 @@ impl<T> Expired<T> {
     pub fn into_inner(self) -> T {
         self.data
     }
+
+    /// Returns the deadline that the expiration was set to.
+    pub fn deadline(&self) -> Instant {
+        self.deadline
+    }
 }