Remove doc reference to old WakerRegistrar

src/sys/unix/selector/poll.rs

@@ -277,7 +277,7 @@ impl SelectorState {
                         }
 
                         // Remove the interest which just got triggered
-                        // the IoSourceState/WakerRegistrar used with this selector will add back
+                        // the IoSourceState/Waker used with this selector will add back
                         // the interest using reregister.
                         poll_fd.events &= !poll_fd.revents;