Remove onDeviceOffBody()

Remove KeyStore#onDeviceOffBody(), since its only caller was removed by
http://ag/24518980.  Also remove
AndroidKeyStoreMaintenance#onDeviceOffBody() which was only called by
KeyStore#onDeviceOffBody().

Bug: 289849354
Test: Build
Change-Id: I3db2672b8038e947a974f703aa2c273ecb65414e
2 files changed