Delete obsolete javadoc warning about pendingTasks() method expensiveness (#11287)

Co-authored-by: Roman Fedorov <roman.fedorov@spikeapp.com>

common/src/main/java/io/netty/util/concurrent/GlobalEventExecutor.java

@@ -129,9 +129,6 @@ public final class GlobalEventExecutor extends AbstractScheduledEventExecutor im
 
     /**
      * Return the number of tasks that are pending for processing.
-     *
-     * <strong>Be aware that this operation may be expensive as it depends on the internal implementation of the
-     * SingleThreadEventExecutor. So use it was care!</strong>
      */
     public int pendingTasks() {
         return taskQueue.size();