Remove task snapshot once the task is move to front.

So it is impossible for any caller to obtain an outdated snapshot,
which may be the cause of vulnerability.

Bug: 305882849
Test: atest TaskSnapshotPersisterLoaderTest
Test: monitor snapshot file will be deleted after task move to front
Change-Id: I5256fe0f8b6a68a82b269a534d0700c8d5dead09
7 files changed