baseset: remove `set()` definition All my friends are dead.

abstractsmartset: remove `set()` method definition Now that all usages have been removed, we can drop this not so useful part of the API. We can note that the name was wrong all along...

match: check if an object is a baseset using `isascending` instead of `set` The `set()` method is going away.

getset: check if an object is a baseset using `isascending` instead of `set` The `set()` method is going away.

fullreposet: detect smartset using "isascending" instead of "set" The `.set()` function is going away.

fullreposet: drop custom sets but not smartsets detection All custom classes use by revsets are smartsets now. We drop the special-casing.

addset: drop `.set()` usage during iteration We can use the containment check directly.

baseset: access `_set` directly for containment check The `.set()` method is going away.

baseset: make `_set` a property cache This will remove the need for `baseset.set()`.

graphnode: remove usage of `set()` All smartset classes have fast lookup, so this function will be removed soon.