Add secdiscard command for secure deletion of files

This is used by LockSettingsService to delete sensitive credential files.

Bug: 34600579
Test: manual - change device lock under synthetic password, verify
      old data on disk is erased.

Change-Id: I5e11b559ad8818bd2ad2b321d67d21477aab7555
Merged-In: I5e11b559ad8818bd2ad2b321d67d21477aab7555
5 files changed