Deprecate second parameter of wxSlider::SetTickFreq().

This parameter was never needed nor properly documented. Simply remove it from
SetTickFreq() and keep the overload still taking it for backwards
compatibility only.

Closes #12907.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66844 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/slider_osx.cpp

@@ -206,7 +206,7 @@ void wxSlider::SetRange(int minValue, int maxValue)
 }
 
 // For trackbars only
-void wxSlider::SetTickFreq(int n, int WXUNUSED(pos))
+void wxSlider::DoSetTickFreq(int n)
 {
     // TODO
     m_tickFreq = n;