Each action set now has an id of its own, assigned when the set is made
(Default Actions, New Set, Begin Recording on an empty panel) and when it
is loaded from the saved preferences. The id is not saved.
The question Delete Selection asks about sets holds their ids, and
ui.actionSet.delete takes ids in place of all: OK deletes the asked sets
wherever they are now, and deletes nothing when one of them no longer
exists. Before, the question matched sets by the list of names, so with
two sets of the same name, or a new set made under the asked one's name
while the question was open, OK could delete a set it did not ask about.