Fix an over-eager removal of a Celery task arg

In a previous commit, I removed the deprecated `lottery_config` argument
from `run_lottery`, thinking I could safely just deprecate old messages
by capturing `lottery_config` with `**kwargs`.

Looking at this code, I now realize that `lottery_config` is being
passed conditionally.

To safely keep the lottery running on all current trips I need to:

1. Deploy this code
2. Restart Celery workers
3. Revoke all open messages identified by `trip.lottery_task_id`

Step 3 can be accomplished by just editing all open lottery trips,
making the close time marginally different.

ws/signals/signup_signals.py

@@ -105,6 +105,7 @@ def revoke_existing_task(sender, instance, raw, using, update_fields, **kwargs):
     except sender.DoesNotExist:  # New trip, initiated with no task
         return
 
+    # TODO: There's a race condition here; we should lock `trip` exclusively
     new_close_time = instance.signups_close_at != trip.signups_close_at
     needs_revoke = new_close_time or trip.algorithm != 'lottery'
     if trip.lottery_task_id and needs_revoke:
@@ -132,9 +133,7 @@ def add_lottery_task(sender, instance, created, raw, using, update_fields, **kwa
         return  # Only new lottery trips get a new task
 
     try:
-        task_id = tasks.run_lottery.apply_async(
-            (trip.pk, None), eta=trip.signups_close_at
-        )
+        task_id = tasks.run_lottery.apply_async((trip.pk,), eta=trip.signups_close_at)
     except OperationalError:
         logger.error("Failed to make lottery task for trip %s", trip.pk)
     else:

ws/tasks.py

@@ -289,13 +289,7 @@ def purge_old_medical_data():
 
 
 @mutex_task('single_trip_lottery-{trip_id}')
-def run_lottery(
-    trip_id: int,
-    # NOTE: Can delete `kwargs` later.
-    # This exists to handle messages which are already queued,
-    # and may include the unused `lottery_config` argument
-    **_kwargs,
-):
+def run_lottery(trip_id: int):
     """Run a lottery algorithm for the given trip (idempotent).
 
     If running on a trip that isn't in lottery mode, this won't make