[request] drop the user argument for set_session
I see no code nor test that use this optional argument. removing it help to
clean the session code. The set_session function will soon be deprecated anyway (at the
same time than the dbapi)
related to #2503918
What's new in CubicWeb 4.0?
============================
API changes
-----------
* ``RepositorySessionManager.postlogin`` is now called with two arguments,
request and session. And this now happens before the session is linked to the
request.
* ``SessionManager`` and ``AuthenticationManager`` now take a repo object at
initialization time instead of a vreg.
* The ``async`` argument of ``_cw.call_service`` have been dropped. All call are
now synchronous. The zmq notification bus looks like a good replacement for
most async usecase.
* ``repo.stats()`` is now deprecated. The same information are available through
a service (``_cw.call_service('repo_stats')``)
* ``repo.gc_stats()`` is now deprecated. The same information are available through
a service (``_cw.call_service('repo_gc_stats')``)
* ``request.set_session`` no longer takes an optional ``user`` argument.
Deprecated Code Drops
----------------------
* The ldapuser source has been dropped. ldapfeed is the only official source
remaining for ldap.
* session.hijack_user mechanism has been dropped.