Remove a workaround for ArangoDB Java drive bug

[wajda]

https://github.com/AbsaOSS/spline/blob/release/0.7/producer-services/src/main/scala/za/co/absa/spline/producer/service/repo/ExecutionProducerRepositoryImpl.scala#L47

Change the type parameter from Any to String and remove unnecessary mapping when arangodb/arangodb-java-driver#411 is merged