[blob-service] Minor AWS cleanups
Summary:
By the way of D8959, performed some minor cleanups in blob codebase.
- Recently noticed that aws_sdk_{dynamodb,s3}::Client already have Arc inside, so we don't need to wrap it with Arc again.
- Also deleted unnecessary aws_types dependency. The type we're using is already included in aws_client. > It probably wasn't in the past and that's why it was added, but now it's not needed anymore.
Plus some very minor fixes to fix Clippy warns.
Depends on D8959
Test Plan: Blob service compiles and runs
Reviewers: michal, varun, patryk, jon
Reviewed By: michal
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D8961