migrations: Subscription.is_user_active denormalization - final step.

With the previous two commits deployed, we're ready to use the
denormalization to optimize the query.

With dev environment db prepared using
./manage.py populate_db --extra-users=2000 --extra-streams=400
this takes the execution time of the query in
bulk_get_subscriber_user_ids from 1.5-1.6s to 0.4-0.5s on my machine.

zerver/lib/actions.py

@@ -3161,12 +3161,10 @@ def bulk_get_subscriber_user_ids(
             zerver_subscription.user_profile_id
         FROM
             zerver_subscription
-        INNER JOIN zerver_userprofile ON
-            zerver_userprofile.id = zerver_subscription.user_profile_id
         WHERE
             zerver_subscription.recipient_id in %(recipient_ids)s AND
             zerver_subscription.active AND
-            zerver_userprofile.is_active
+            zerver_subscription.is_user_active
         ORDER BY
             zerver_subscription.recipient_id,
             zerver_subscription.user_profile_id