revset: remove useless extpredicate class (API)...
revset: remove useless extpredicate class (API)
Previous patch makes this classes useless by replacing it with
revsetpredicate of registrar.
BTW, extpredicate itself has already been broken by that patch,
because revsetpredicate of registrar doesn't have compatibility with
original predicate (derived from funcregistrar of registrar), in fact.