Secure => global bubble settings pt 1

Follow up to http://ag/8222583
- Remove Secure.NOTIFICATION_BUBBLES from backup.
- Replace references to Secure.NOTIFICATION_BUBBLES with
Global.NOTIFICATION_BUBBLES
- Update tests

Fixes: 136034310
Bug: 129158983
Test: atest SystemUITests
Test: manual - work profile bubbles show up
Change-Id: I0c1956272e9d18bcd2e13c6658ca8925cedfcef5