Remove the lfs_storage_project helper

What does this MR do?

This appears to be obsolete - according to this issue: #122002 (closed), all the necessary work has already been done for us to stop using lfs_storage_project.

Remove it and see what breaks!

This includes removing some code I only got added today, refusing to run the LFS object cleanup if we're a fork root. No changelog needed, I think, since it was only just added.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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Closes #122002 (closed)