Call `expunge` in delta/longpoll endpoint to prevent long-lived transaction
Call `expunge` in delta/longpoll endpoint to prevent long-lived transaction

References to g.namespace in the delta/longpoll endpoint after closing the
session may be causing a long-lived session. Expunge the namespace object
to prevent this, like what we do in the delta/streaming endpoint.

jobscore/sync-engine,jobscore/sync-engine,jobscore/sync-engine,jobscore/sync-engine