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/os2/slider.cpp

@@ -1074,7 +1074,7 @@ void wxSlider::SetTick(
 } // end of wxSlider::SetTick
 
 // For trackbars only
-void wxSlider::SetTickFreq( int n, int WXUNUSED(nPos) )
+void wxSlider::DoSetTickFreq( int n )
 {
     SLDCDATA  vSlData;
     WNDPARAMS vWndParams;