Fix response of 'DeleteDataObjects' protocol

Type of change

• Bug Fix
• Feature

Does this introduce a change in the core logic?

• [No]

Does this introduce a change in the cloud provider implementation, if so which cloud?

• AWS
• Azure
• GCP
• IBM

Updates description?

According to ETP specification protocol DeleteDataObjects should return map of objects which were successfully deleted, but currently it's empty.

Issue: #63 (closed)