chore: remove unused variable in removeWindow (#16715)

atom/browser/api/atom_api_top_level_window.cc

@@ -660,8 +660,6 @@ void TopLevelWindow::SetMenu(v8::Isolate* isolate, v8::Local<v8::Value> value) {
 }
 
 void TopLevelWindow::RemoveMenu() {
-  mate::Handle<Menu> menu;
-
   menu_.Reset();
   window_->SetMenu(nullptr);
 }