[Feature flag] Cleanup manage_compliance_frameworks_modals_refactor

What does this MR do and why?

Clean up feature flag manage_compliance_frameworks_modals_refactor and simplify FF related code.

Remove old controller+views for the create/edit forms + related JS.

Screenshots or screen recordings

n/a

How to set up and validate locally

Feature.enable(:manage_compliance_frameworks_modals_refactor)
Feature.disable(:manage_compliance_frameworks_modals_refactor)

1. Visit a top level group, with owner access
2. Click Settings -> General
3. Scroll down and expand Compliance Frameworks
4. Add / Edit flows now use modal instead of full page redirects, regardless of whether the feature flag is enabled or not.

and

1. Visit a top level group, with owner access
2. Click Security -> Compliance report -> Frameworks
3. Add / Edit flows from within the report now use modal instead of full page redirects, regardless of whether the feature flag is enabled or not.

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 #389735 (closed)