tests/artifacts/PURPOSE

rebase: delete seemingly unnecessary needupdate()

This seemed to be about checking that the user hasn't updated away
when we asked them to resolve merge conflicts. These days we call
`cmdutil.checkunfinished()` and refuse to update, so the user
shouldn't be able to get into this state.

`test-rebase-interruptions.t` actually has some tests where it
disables the rebase extension in order to be allowed to do some of
these updates. That still passes, but I wouldn't personally haved
cared if that failed.

Differential Revision: https://phab.mercurial-scm.org/D7825

This directory is meant to cache artifacts useful for tests (such as bundle).

Those artifacts need to be cached because they are slow to regenerate on each
test but too large to be tracked within the repository. They are not expected
to change between each run and can be cached.

The `./scripts/` contains code to generate the artifact while the `cache`
directory contains resulting artifact.