base/data_type_validated.h: remove as an ODR risk from poor layering

This provides a template Validated<T>, which interacts with the "data layer" API.

The ONLY uses of this thing are `Validated<BSONObj>`, which is defined in a far away disconnected file rpc/object_check.h, which is really not obvious.

Failing to include rpc/object_check.h yields an ODR violation when one then tries to use `Validated<BSONObj>`.

There's no need for the acrobatics. We can just have a `mongo::rpc::ValidatedBSONObj` data type defined in rpc/object_check.h that doesn't have any of these risks.