KeyMint AIDL tweaks

- Describe 3DES requirements
- Remove references to non-existent getKeyCharacteristics() entrypoint
- Remove references to non-existent attestKey() entrypoint
- Remove mention of asymmetric verification operations
- Remove text describing incomplete update()
- Remove text discussing padding for ECDSA
- EC keys can't encrypt/decrypt
- Force use of curve not key size for EC keys
- Drop TODO re: CBOR encoding of wrapped key
- Indicate caller-provided nonces must have correct size
- Add more reference to IKeyMintOperation
- Align parameter names with signatures
- Correct MIN_MAC_LENGTH error code
- Make CREATION_DATETIME consistently optional
- Describe use of MGF1 digest option
- Fix typos

Test: VtsKeyMintAidlTargetTest (CF)
Change-Id: Ie01b99d33be7336e872bf24a7761a3ac5b1d584c