removed a redundant include from AppTask.cpp (#32803)

diff --git a/examples/window-app/silabs/src/AppTask.cpp b/examples/window-app/silabs/src/AppTask.cpp
index f255bed..214a405 100644
--- a/examples/window-app/silabs/src/AppTask.cpp
+++ b/examples/window-app/silabs/src/AppTask.cpp
@@ -23,7 +23,6 @@
 
 #include "WindowManager.h"
 
-#include <app/clusters/on-off-server/on-off-server.h>
 #include <app/server/OnboardingCodesUtil.h>
 #include <app/server/Server.h>
 #include <app/util/attribute-storage.h>