Use generic code for wheel scrolling on wxGTK as discussed on wx-dev a couple weeks ago

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@47783 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/scrlwing.cpp

@@ -267,14 +267,11 @@ bool wxScrollHelperEvtHandler::ProcessEvent(wxEvent& event)
         m_scrollHelper->HandleOnMouseLeave((wxMouseEvent &)event);
     }
 #if wxUSE_MOUSEWHEEL
-    // Use GTK's own scroll wheel handling in GtkScrolledWindow
-#ifndef __WXGTK20__
     else if ( evType == wxEVT_MOUSEWHEEL )
     {
         m_scrollHelper->HandleOnMouseWheel((wxMouseEvent &)event);
         return true;
     }
-#endif
 #endif // wxUSE_MOUSEWHEEL
     else if ( evType == wxEVT_CHAR )
     {