Notifications: removing a message causes unwanted unknown message notification

[agjohnson]

I noticed that when removing a message in code, or altering the message id, that all of the old messages stored in the database but not dismissed are still emit to the user as an Unknown message.

To reproduce:

• Add a notification to your user, like the new dashboard notification
• Change the id of the notification in the database or delete the message in code
• Reload and you should receive this notification:

We should probably just raise an internal error, not message the user in this scenario. Sending a message is unexpected.

[humitos]

On the user side, we should show nothing (no notification at all). On the application side, we should log a Sentry event/New Relic log. We can't raise an exception because the production DB could have old IDs that were deleted in code but they are still in the DB.