Align KeyMint AIDL with usage

 - Make HardwareAuthToken nullable on begin()
 - Drop unused vestigial performOperation() entrypoint
 - Drop unused Tag::BLOB_USAGE_REQUIREMENTS

Test: TreeHugger, VtsKeyMintAidlTargetTest (CF)
Change-Id: I577ac04d843ee6d03cbfb99e56ef3e69eb034532
7 files changed