remove unused signal displayPowerChanged (#22719)

selfdrive/ui/qt/home.h

@@ -44,7 +44,6 @@ signals:
   void closeSettings();
 
   // forwarded signals
-  void displayPowerChanged(bool on);
   void update(const UIState &s);
   void offroadTransitionSignal(bool offroad);
 

selfdrive/ui/qt/window.cc

@@ -15,7 +15,6 @@ MainWindow::MainWindow(QWidget *parent) : QWidget(parent) {
   QObject::connect(&qs, &QUIState::uiUpdate, homeWindow, &HomeWindow::update);
   QObject::connect(&qs, &QUIState::offroadTransition, homeWindow, &HomeWindow::offroadTransition);
   QObject::connect(&qs, &QUIState::offroadTransition, homeWindow, &HomeWindow::offroadTransitionSignal);
-  QObject::connect(&device, &Device::displayPowerChanged, homeWindow, &HomeWindow::displayPowerChanged);
 
   settingsWindow = new SettingsWindow(this);
   main_layout->addWidget(settingsWindow);