bundle: quick fix to ludicrous performance penalty

We tried a `hg bundle --base ':(tip^)' --rev 'all()'` on a large repository and
it spent 3 minutes on this 2 list comprehensions. This change remove this cost.

There are still a lot of low hanging fruits as the command still take 30
seconds. However this is a trivial patch with a massive speedup so I'll just
sent it.
11 jobs for topic/default/bundle-speedup in 21 minutes and 50 seconds (queued for 9 seconds)