I clicked send on this note, before I saw the deluge.
What we would not want is to hide closure notices to the cc recipients on the issue. We would not want to remove bugs@ from the issue itself. And anyone reconfirming a ticket is not stale is going to the bugs@ notification list.
My only thought on avoiding this in the future is to suspend the bugs@ list entirely for a several minute period while the mass update notifications are sent. Then restore the normal list behavior.
If you simply want to hide this mass update, I would unthread your mail reader, and mass select and delete all email notices during that small 5 minute window.
Another option, I kept with threading, and mass deleted only those updates with no other notices in a multi-year period. I'm now going back over some 70 closures which had an active discussion at some point in the not so distant past.
Sorry for this somewhat painful side effect of this cleanup operation. Since we've decided most other updates will employ some level of manual scrutiny and intervention, there shouldn't be another burst of notices for some years to come.