OSX specific, related to the wxWidgets 3.1.4: Fixed wrong UI-scaling

(wxWidgets 3.1.4 can binding of wxEVT_DPI_CHANGED now, so it was called msw_rescale() for most of the controls redundantly)

+ Fixed update of the DoubleSlider after changing of the system color

src/slic3r/GUI/OG_CustomCtrl.cpp

@@ -360,6 +360,9 @@ void OG_CustomCtrl::correct_widgets_position(wxSizer* widget, const Line& line,
 
 void OG_CustomCtrl::msw_rescale()
 {
+#ifdef __WXOSX__
+    return;
+#endif
     m_font      = wxGetApp().normal_font();
     m_em_unit   = em_unit(m_parent);
     m_v_gap     = lround(1.0 * m_em_unit);
@@ -381,7 +384,6 @@ void OG_CustomCtrl::msw_rescale()
 
 void OG_CustomCtrl::sys_color_changed()
 {
-    msw_rescale();
 }
 
 OG_CustomCtrl::CtrlLine::CtrlLine(  wxCoord         height,