Remove interface holder from BaseTestValidator
Remove interface holder from BaseTestValidator

The tests that inherit from BaseTestValidator have all been
refactored to remove the old db interfaces, so the last
step here is to remove the interface holder that was
being passed around.

fedspendingtransparency/data-act-broker-backend,chambers-brian/SIG_Digital-Strategy_SI_ODP_Backend,chambers-brian/SIG_Digital-Strategy_SI_ODP_Backend,fedspendingtransparency/data-act-broker-backend