Remove the software-specific Decrypt16BytesBlock and Encrypt16BytesBlock traits

They assume blocks are encrypted/decrypted one at a time. To avoid one syscall
per block, it is preferable to encrypt/decrypt the data at once.

Change-Id: I795c8f5b7901a1b55fa3b06fa45fe57ab19d06ea

libraries/crypto/tests/aesavs.rs

@@ -16,7 +16,7 @@
 ///
 /// See also https://csrc.nist.gov/CSRC/media/Projects/Cryptographic-Algorithm-Validation-Program/documents/aes/AESAVS.pdf
 use arrayref::array_ref;
-use crypto::{aes256, Decrypt16BytesBlock, Encrypt16BytesBlock};
+use crypto::aes256;
 use regex::Regex;
 use std::fs::File;
 use std::io::{BufRead, BufReader};