Remove references to service classes in the src/test/java

[ashpak-shaikh]

With the migration to groovy style tests, we do not need the test service classes in test/java. The services are in the following package https://github.com/graph-quilt/graphql-orchestrator-java/tree/master/src/test/java/com/intuit/graphql/orchestrator
An example would be BookService

Delete these service class and migrate all the test referring to these services to groovy. Example of groovy test
https://github.com/graph-quilt/graphql-orchestrator-java/blob/master/src/test/groovy/com/intuit/graphql/orchestrator/integration/TopLevelStitchingSpec.groovy
More tests in this package

[tasneemkoushar]

@ashpak-shaikh can I take this issue?