Delete unused methods from NotePolicy

What does this MR do and why?

This MR removes the access_level and lookup_access_level methods from the NotePolicy file because these methods are not being called anywhere and should be deleted.

This cleanup needs to happen so we can standardize how access levels are determined across GroupPolicy and ProjectPolicy https://gitlab.com/gitlab-org/gitlab/-/work_items/583655

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.