Remove unused package_verifier_state setting.

This was added during O development but never used. (It was going to
be used to store whether GPP was enabled, but the relevant settings
screen was implemented in GMS Core instead. See b/31002801, especially
comment 7 onwards.)

It now serves no purpose other than misinformation.

I also updated the test so when backup of settings is misconfigured
the error message tells you which ones.

Change-Id: Ib5e9a9ced1d1a43844889192cefddeec335f9f78
Fix: 34259924
Bug: 135751498
Test: Builds
Test: atest SettingsProviderTest