Node.js Crypto: Error Message Hygiene

After I added initial support for Authenticated Encryption to Node.js last year, someone else built on this and extended the API with the ability to use Associated Data, putting the AD into AEAD. I toyed with it a little and found that the generated errors could use some love.

Find the PR and diff on Github: https://github.com/nodejs/node-v0.x-archive/pull/7502