Remove unused shutdown() function from WebSchedulerImpl.

content/renderer/scheduler/web_scheduler_impl.cc

Index: content/renderer/scheduler/web_scheduler_impl.cc
diff --git a/content/renderer/scheduler/web_scheduler_impl.cc b/content/renderer/scheduler/web_scheduler_impl.cc
index 550be3b1ba657d557d1936e89c75e75a6c00fe34..efab3e2404e49e39142093fc1456db172d188f43 100644
--- a/content/renderer/scheduler/web_scheduler_impl.cc
+++ b/content/renderer/scheduler/web_scheduler_impl.cc
@@ -99,8 +99,4 @@ void WebSchedulerImpl::postTimerTask(
       base::TimeDelta::FromMilliseconds(delayMs));
 }
 
-void WebSchedulerImpl::shutdown() {
-  // TODO(rmcilroy): Delete this method once the blink side is removed.
-}
-
 }  // namespace content