Remove an invalid assertion in fire_timer.

It's not clear to me if this is something we should expect to happen, but it
does indeed happen, so we should disable the assertion while we investigate.

Fixes #9984.

components/script/timers.rs

@@ -176,7 +176,10 @@ impl OneshotTimers {
         let base_time = self.base_time();
 
         // Since the event id was the expected one, at least one timer should be due.
-        assert!(base_time >= self.timers.borrow().last().unwrap().scheduled_for);
+        if base_time < self.timers.borrow().last().unwrap().scheduled_for {
+            warn!("Unexpected timing!");
+            return;
+        }
 
         // select timers to run to prevent firing timers
         // that were installed during fire of another timer