context: revert workingctx.ancestors() followfirst option It was introduced by mistake in 352053e6cd8e.

graphlog: fix --follow-first --rev combinations This solves a similar problem than the previous --follow/--rev patch. This time we need changelog.ancestors()/descendants() filtering on first parent. Duplicating the code looked better than introducing keyword arguments. Besides, the ancestors() version was already implemented in follow() revset.