Latest tenacity release adds some internal changes that broke the
mocking of sleep calls in tests.
Fix it by directly mocking time.sleep (was not working previously).
Legacy Lister classes from the swh.lister.core mdule are no longer
used in swh-lister codebase so it is time to remove them.
Also remove lister CLI options related to legacy Lister API.
As a consequence, the following requirements are no longer needed:
arrow, SQLAlchemy, sqlalchemy-stubs and testing.postgresql.
Closes T2442
This allows us to actually run the lister instantiation code instead of relying
on the underlying structure of the lister object. In turn, this allows future
listers to use the scheduler right in their __init__.
