Removed unused variables in PerformBackupTask#finalizeBackup()

The unused variables got left behind after changes in ag/1841867.

This replicates ag/2077691 in RefactoredBackupManagerService.

Bug: 35994670
Test: it builds
Change-Id: Ic28719dafb83542d7e4c73cb48508d6792d10174
1 file changed