hidden: drop the hidden cache logic
The improvement in time complexitty and the speed-up in computation is large
enough that the has little use now. Its update time can even gets in the way. So
we drop it.
This will allow us to unify the static/dynamic blockers logic in the next
changeset.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.