_orderedsetmixin: drop this now unused class All my friends are dead.

spanset: drop _orderedsetmixin inheritance The min/max method are as well provided by abstractsmartset.

orderedlazyset: drop this now unused class All my friends are dead.

_descendant: use filteredset instead of orderedlazyset The orderedlazyset class is going away. Filteredset gives the same service.

addset: use the base implementation for ascending and descending

addset: use base implementation for __filter__

addset: use base implementation for __add__

addset: use base implementation for __sub__

addset: use base implementation for __and__

addset: promote to real smartset Better revset performance are also achieved with less overlay. There is no good reason for addset to not be a smartset. We can replace the `_orderedsetmixin` inheritance since `abstractsmartset` has efficient min and max too.