[services] Backup - Connect to Blob - Remove c++ part

Summary:
Depends on D4870

Removing c++ part responsible for handling the inner blob client calls in the backup service. Instead of using c++ for this, we agreed on using rust.

Test Plan: backup builds

Reviewers: tomek, jon

Reviewed By: tomek

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D4885