This diff introduces extracting the `deleteQueueIfEmpty` calling for the DeliveryBroker into a separate function to call it in the following D6626 from the Rust gRPC handler.
The reason for extracting is disabling messages persisting in the DynamoDB database by the config flag introduced in the D6622. In the following D6626, we will call `deleteQueueIfEmpty` function, but skip to remove the messages from the database if the config flag from D6622 is presented.
Linear task: [[ https://linear.app/comm/issue/ENG-2641/disabling-messages-persistence-in-the-database-in-tunnelbroker | ENG-2641 ]]