The feature of cancelling waiting holds depends on circulation rules. It may not be used at all. So when there are no cancellation requests tab whe should not show the tab in circ/waitingreserves.pl
I have been thinking about a workaround but it appears it is very tricky to resolve for a very low impact. Checking the number of waiting reserves appears not to be a good solution since knowing there is no reserves is an interesting information From the circulation rules, we should be able to infer that absolutely no one has the right to cancel holds, however such a proof is hard to provide. Hence it is probably better to close the ticket