Handle Account Manager database downgrade.

Currenlty AM database downgrade causes crash loop in system service
during boot.
New behaivour is deleting old data and creating empty database.
Downgrade shouldn't happen in production, but may affect developers who
didn't wipe device data.

Bug: 118399665
Test: manual
Change-Id: I7882e9ba4e485c3874360aef9d21d849565879d2