JCLOUDS-750 Revert customizing FieldNamingStrategy in favor of tighter contract on @SerializedNames.

In  5b6f1e9, we added the ability to customize the FieldNamingStrategy, so that you can control the serialized names on auto-value types. I've added code to propagate the same names used for deserialization to also be used for serialization. With this in, customizing FieldNamingStrategy is no longer needed, and should be removed.
Part of the revert. Contract in gson says return null if you don't know the
name.