unbundle: don't advance bookmarks (issue4322) (BC)

This behavior didn't make much sense and interacts badly with things
that use unbundle internally like shelve. Presumably, the original
rationale was that since bundles didn't contain bookmarks, this gave a
sense of keeping bookmarks up-to-date like would happen with a
corresponding pull. However, since it only updated the current active
bookmark, and bare update already did that anyway, this is pretty
slim.

Notably, the corresponding test actually works better without this
feature.

--HG--
branch : stable