[services][blob] Handle removing blobs

Summary:
Implemented the Remove RPC handler.

C++ counterpart

Depends on D5701

Test Plan:

1. Create the blob using e.g. C++ service, or in any other way.
2. Remove the blob using Rust implementation
3. Ensure it is deleted in DynamoDB (both tables) and S3

Reviewers: varun, jon, tomek, marcin

Reviewed By: varun, tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D5702