Remove unnecessary wxBusyCursor from the treectrl sample

This was added way back in 618a5e382a (Applied Greg's patch to tree
control and related., 2001-08-18) for some reason, but probably was
never needed and definitely isn't any more.

samples/treectrl/treetest.cpp

@@ -978,7 +978,6 @@ void MyTreeCtrl::CreateImageList(int size)
     wxImageList *images = new wxImageList(size, size, true);
 
     // should correspond to TreeCtrlIcon_xxx enum
-    wxBusyCursor wait;
     wxIcon icons[5];
 
     if (m_alternateImages)