Removed never happening condition (#14536)

src/Avalonia.Base/Threading/Dispatcher.Queue.cs

@@ -65,7 +65,7 @@ public partial class Dispatcher
                 job = _queue.Peek();
             if (job == null)
                 return;
-            if (priority != null && job.Priority < priority.Value)
+            if (job.Priority < priority.Value)
                 return;
             ExecuteJob(job);
         }