Reset backup tracking in response to transport data-wipe notification

When attempting a backup, the transport may inform us that the backend is in an
uninitialized state.  This typically means that the device's data has been wiped
after a period [e.g. 90 days] of inactivity.  This means that we need to
re-store all data subject to backup, and all of our incremental state tracking
on the device is now stale.

In response, we wipe all of our recorded backup state and restart the backup
pass on all participants.