docs(db): remove docs for autoIndexId
docs(db): remove docs for autoIndexId

We've already said this was off since 2.2. Since we don't even support
below 2.4, this isn't deprecated so much as no longer allowed.
Removing it from our documentation.

Fixes NODE-1428

mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native