Remove renaming license approval status migration code

What does this MR do and why?

• Remove feature flag code for :lc_remove_legacy_approval_status
• Remove references in frontend, backend, and frontend/backend unit tests

Screenshots or screen recordings

Before and After are the same. I can demo if required.

Note: The weird "X more" artifact seems to be already in production related to some style changes. I will follow up as a separate issue unrelated to these changes.

How to set up and validate locally

• Reach out to me for a demo, otherwise setting up is a process.
• Clone the https://gitlab.com/gitlab-examples/security/security-reports project locally
• Set up Allowed/Denied licenses in https://<localhost>/<group>/<project>/-/licenses#policies
• Create a new MR
• See License compliance widget
• Visit 'Licenses' tab under the Pipeline view

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #356206 (closed)