Instead of alternative signature and merkle tree, authfs will use
.fsv_meta files, which are installed to the system partition with
PRODUCT_SYSTEM_FSVERITY_GENERATE_METADATA Makefile.
Bug: 205987437
Test: atest ComposHostTestCases AuthFsTestCase
Test: run "atest ." inside authfs/tests
Change-Id: Ia9db78663e0e322c7a59305c67ac5b84716d8efe