Scrolling fixes for RTL layout with GTK3

Avoid some positioning hacks, they are not needed with GTK3

src/generic/listctrl.cpp

@@ -1042,7 +1042,7 @@ void wxListHeaderWindow::AdjustDC(wxDC& dc)
     dc.GetDeviceOrigin( &org_x, &org_y );
 
     // account for the horz scrollbar offset
-#ifdef __WXGTK__
+#if defined(__WXGTK__) && !defined(__WXGTK3__)
     if (GetLayoutDirection() == wxLayout_RightToLeft)
     {
         // Maybe we just have to check for m_signX

src/generic/scrlwing.cpp

@@ -655,7 +655,7 @@ int wxScrollHelperBase::CalcScrollInc(wxScrollWinEvent& event)
 void wxScrollHelperBase::DoPrepareDC(wxDC& dc)
 {
     wxPoint pt = dc.GetDeviceOrigin();
-#ifdef __WXGTK__
+#if defined(__WXGTK__) && !defined(__WXGTK3__)
     // It may actually be correct to always query
     // the m_sign from the DC here, but I leave the
     // #ifdef GTK for now.

src/gtk/win_gtk.cpp

@@ -476,8 +476,10 @@ static void scroll_adjust(GtkWidget* widget, void* data)
 void wxPizza::scroll(int dx, int dy)
 {
     GtkWidget* widget = GTK_WIDGET(this);
+#ifndef __WXGTK3__
     if (gtk_widget_get_direction(widget) == GTK_TEXT_DIR_RTL)
         dx = -dx;
+#endif
     m_scroll_x -= dx;
     m_scroll_y -= dy;
     GdkWindow* window = gtk_widget_get_window(widget);