Remove OPENSSL_NO_SHA512

Changes were made by running

find . -type f -name *.c | xargs unifdef -m -U OPENSSL_NO_SHA512
find . -type f -name *.h | xargs unifdef -m -U OPENSSL_NO_SHA512

Change-Id: I5c8a89384c865423aa7b549470068ef18161bce4
Reviewed-on: https://boringssl-review.googlesource.com/1379
Reviewed-by: Adam Langley <agl@google.com>