Remove SSL_CIPHER_ALGORITHM2_AEAD.

All ciphers are implemented by an EVP_AEAD.

Change-Id: Ifa754599a34e16bf97e1a4b84a271c6d45462c7c
Reviewed-on: https://boringssl-review.googlesource.com/4958
Reviewed-by: Adam Langley <agl@google.com>