Remove the per-user session limit

This feature was originally introduced by
f961ffd9c7 as a fix for FS#12898
<https://bugs.archlinux.org/task/12898>.

As of today, it is broken because of the `q.SessionID IS NULL` condition
in the WHERE clause, which can’t be true because SessionID is not
nullable. As a consequence, the session limit was not applied.

The fact the absence of the session limit hasn’t caused any issue so
far, and hadn’t even been noticed, suggests the feature is unneeded.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

aurweb/routers/sso.py

@@ -56,7 +56,7 @@ def open_session(request, conn, user_id):
         raise HTTPException(status_code=403, detail=_('Account suspended'))
         # TODO This is a terrible message because it could imply the attempt at
         #      logging in just caused the suspension.
-    # TODO apply [options] max_sessions_per_user
+
     sid = uuid.uuid4().hex
     conn.execute(Sessions.insert().values(
         UsersID=user_id,