Removing remaining code around ENABLE_DATABASE_RESTORE

ENABLE_DATABASE_RESTORE feature is already removed
Also migrating some tests from BackupRestoreTest to RestoreDbTaskTest

Bug: 270392706
Test: Presubmit
Flag: N/A
Change-Id: I71822bbc2232008b3d2b4b9fbed0db5d889591e4
9 files changed