Implement /delivery/unregister_consumer API method

Summary:
This API method deletes a queue.

Ref T1210

Test Plan:
Post a JSON payload to http://localhost:5000/delivery/unregister_consumer

{
	"key": "b94c656b-5ee6-4135-8b8b-a787ef5ab5a6"
}

The queue delivery-b94c656b-5ee6-4135-8b8b-a787ef5ab5a6 was well deleted.

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1210

Differential Revision: https://devcentral.nasqueron.org/D992