Delete unused duplicate libc_util.py file (#6579)

## Summary
 
Delete an unused duplicate libc_util.py file. The active version is at
`invokeai/backend/model_manager/libc_util.py`

## QA Instructions

I ran a smoke test to confirm that memory snapshotting still works.

## Merge Plan

- [x] Change target branch to `main` before merging.

## Checklist

- [x] _The PR has a short but descriptive title, suitable for a
changelog_
- [x] _Tests added / updated (if applicable)_
- [x] _Documentation added / updated (if applicable)_