refactor: keyboard layout applet: return to Properties-based QML API

As all layouts names are now stored in Property on client side, there is
no need for KeyboardLayoutDBusInterface::getLayoutLongName() method any
more.

keyboard_layout.cpp

@@ -222,11 +222,6 @@ uint KeyboardLayoutDBusInterface::getLayout() const
     return m_xkb->currentLayout();
 }
 
-QString KeyboardLayoutDBusInterface::getLayoutLongName() const
-{
-    return translatedLayout(m_xkb->layoutName());
-}
-
 QVector<KeyboardLayoutDBusInterface::LayoutNames> KeyboardLayoutDBusInterface::getLayoutsList() const
 {
     // TODO: - should be handled by layout applet itself, it has nothing to do with KWin

keyboard_layout.h

@@ -86,7 +86,6 @@ public Q_SLOTS:
     void switchToPreviousLayout();
     bool setLayout(uint index);
     uint getLayout() const;
-    QString getLayoutLongName() const;
     QVector<LayoutNames> getLayoutsList() const;
 
 Q_SIGNALS: