impr: Keyboard Layout DBus API: drop excessive method arguments

It's enough to give info about current layout only or all the layouts
altogether, so no need to pass layout to asqure in an argument.

P-W part:
impr: Keyboard Layout plugin: drop excessive DBus API method arguments

keyboard_layout.cpp

@@ -77,7 +77,7 @@ void KeyboardLayout::initDBusInterface()
     m_dbusInterface = new KeyboardLayoutDBusInterface(m_xkb, this);
     connect(this, &KeyboardLayout::layoutChanged, m_dbusInterface,
         [this] {
-            emit m_dbusInterface->currentLayoutChanged(m_xkb->layoutName());
+            emit m_dbusInterface->layoutChanged(m_xkb->layoutName());
         }
     );
     // TODO: the signal might be emitted even if the list didn't change
@@ -319,17 +319,22 @@ bool KeyboardLayoutDBusInterface::setLayout(const QString &layout)
     return true;
 }
 
-QString KeyboardLayoutDBusInterface::getCurrentLayout()
+QString KeyboardLayoutDBusInterface::getLayout() const
 {
     return m_xkb->layoutName();
 }
 
-QString KeyboardLayoutDBusInterface::getCurrentLayoutLongName() const
+QString KeyboardLayoutDBusInterface::getLayoutDisplayName() const
+{
+    return m_xkb->layoutShortName();
+}
+
+QString KeyboardLayoutDBusInterface::getLayoutLongName() const
 {
     return translatedLayout(m_xkb->layoutName());
 }
 
-QStringList KeyboardLayoutDBusInterface::getLayoutsList()
+QStringList KeyboardLayoutDBusInterface::getLayoutsList() const
 {
     const auto layouts = m_xkb->layoutNames();
     QStringList ret;
@@ -339,12 +344,4 @@ QStringList KeyboardLayoutDBusInterface::getLayoutsList()
     return ret;
 }
 
-QString KeyboardLayoutDBusInterface::getLayoutDisplayName(const QString &layout)
-{
-    // TODO: remove arguments from the DBus API methods
-    Q_UNUSED(layout)
-
-    return m_xkb->layoutShortName();
-}
-
 }

keyboard_layout.h

@@ -84,13 +84,13 @@ public Q_SLOTS:
     void switchToNextLayout();
     void switchToPreviousLayout();
     bool setLayout(const QString &layout);
-    QString getCurrentLayout();
-    QString getCurrentLayoutLongName() const;
-    QStringList getLayoutsList();
-    QString getLayoutDisplayName(const QString &layout);
+    QString getLayout() const;
+    QString getLayoutDisplayName() const;
+    QString getLayoutLongName() const;
+    QStringList getLayoutsList() const;
 
 Q_SIGNALS:
-    void currentLayoutChanged(QString layout);
+    void layoutChanged(QString layout);
     void layoutListChanged();
 
 private: