May as well. Depending on the implementation chosen in cipher/e_aes.c,
AES_encrypt may or may not be hit, so test this entry point explicitly.

Change-Id: Icb02bf3f4b6e5ecbb9e5111f44fbb1b267ead6c3
Reviewed-on: https://boringssl-review.googlesource.com/5312
Reviewed-by: Adam Langley <agl@google.com>