PerformBackupTask getting 2 IBackupObserver.backupFinished()

Remove IBackupObserver.backupFinished() before
executeNextState(BackupState.FINAL), add test cases to verify it and
format PerformBackupTaskTest.java
Bug: 77272662
Test: make RunFrameworksServicesRoboTests

Change-Id: Ia464d0326437fb8680ab88619829c483e2c1164d
2 files changed