Remove unnecessary commented out test

This test remained since 902725eefe but
should have been simply removed back then, as we return if the item is
null due to a test above.

No real changes.

src/generic/treectlg.cpp

@@ -3790,8 +3790,7 @@ void wxGenericTreeCtrl::OnMouse( wxMouseEvent &event )
             }
 
             // this facilitates multiple-item drag-and-drop
-
-            if ( /* item && */ HasFlag(wxTR_MULTIPLE))
+            if ( HasFlag(wxTR_MULTIPLE))
             {
                 wxArrayTreeItemIds selections;
                 size_t count = GetSelections(selections);