Audit all of our Go code that uses `crypto/aes`.

The implementation is not constant time (and neither is the GHASH provided by crypto/cipher) without AES-NI/PCLMULQDQ or equivalent. I do not believe that we use either in a situation where it matters, but we should double check to confirm this. This affects any uses of the raw primitive, when wrapped in the various block cipher modes, and when used via TLS.

Known uses: