Move the `objects` method to `LfsHelper` so that it is also available to `LfsStorageController`

## What does this MR do?

Move the `objects` method to `LfsHelper` so that it is also available to `LfsStorageController`

It is needed for the `lfs_check_access!` callback when the repository size limit is enabled (EE only).

cc @stanhu @ahanselka 

## Why was this MR needed?

Errors shown here: gitlab-org/gitlab-ce#24392

Discovered thanks to gitlab-com/infrastructure#302

## What are the relevant issue numbers?

Fixes #24392 

Fixes gitlab-com/support-forum#1280

See merge request !7417