Test: Fix imports in DropIndexOperationSpecification

Author: rozza

driver-core/src/test/functional/com/mongodb/operation/DropIndexOperationSpecification.groovy

@@ -34,7 +34,6 @@ import static com.mongodb.ClusterFixture.getBinding
 import static com.mongodb.ClusterFixture.isDiscoverableReplicaSet
 import static com.mongodb.ClusterFixture.isSharded
 import static com.mongodb.ClusterFixture.serverVersionAtLeast
-import static java.util.concurrent.TimeUnit.MILLISECONDS
 import static java.util.concurrent.TimeUnit.SECONDS
 
 class DropIndexOperationSpecification extends OperationFunctionalSpecification {