Keystore 2.0: Untangle GC from Keystore DB.

Notifying the garbage collector directly from the DB breaks the unit
test because the GC implicitly uses the global DB instance.
This moves GC notification outside of the KeystoreDB.

Also remove #[!allow(dead_code)] from database.rs.

Test: keystore2_test
Change-Id: Ia2812d47ccee05309aaa91063d0d99c853596ea1
3 files changed