Delete old failure_counter file when LSKF is changed

When an LSKF-based synthetic password protector is destroyed, all files
belonging to it should be deleted, including the failure_counter file.

Bug: 424597164
Test: atest FrameworksServicesTests:com.android.server.locksettings
Flag: EXEMPT trivial change that should not be flagged since we should
      clean up the file even if the flag goes from ENABLED => DISABLED.
Change-Id: Id95d589e8670914f85ccfdd9199db910c427cd98