With the SDK moving out into its own repository, a lot of the packages
under "helper/" are no longer needed. We still need to keep around just
enough legacy SDK to support the "test" provider and some little bits and
bobs in the backends and provisioners, but a lot of this is now just dead
code.
One of the test provider tests was depending on some validation functions
only because the schema in there was originally copied from a "real"
provider. The validation rules are not actually important for the test,
so I removed them. Otherwise, this removes only dead code.
6b5ca49578