Context: https://linear.app/comm/issue/ENG-2078/notification-rescinds-dont-appear-to-be-working-as-expected
Basically, we shouldn't be sending anything **except** `content-available: 1` in the APS dictionary for `background` notifications. Any alerts/badges/sounds must be sent via `alert` notifications.
Here's a relevant snippet from the documentation:
Background notifications should be "invisible" to the user and **may** get some runtime (based on a bunch of factors including daily app usage, battery life, etc) in order to execute some code.
This change should be a noop because based on my reading/experimentation including this field wasn't updating the badge count anyways. It looks like we've already realized that rescinding notifications and updating badge count need to happen separately given `rescindAndUpdateBadgeCounts(...)` sends both an `alert` and `background` notification.