[backup] Remove gRPC from backup

Summary:

1. Remove gRPC interface of backup service. More info here: ENG-4501, but generally web app will also need to send large files in the future
2. Remove blob gRPC client. Start of ENG-3687
3. Updated Cargo.toml (and run the default formatter)

I decided to do it first instead of first creating backup interface and only then removing the gRPC one but:

• as far as I know the current backup service isn't used anywhere
• I will be able to reuse some database code but it will need to be changed and I don't want to have to change the gRPC code to match, if it's going to be removed anyway

Test Plan:

1. cargo build
2. Built the docker image

Reviewers: bartek, patryk, jon

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8796