Remove `compliance_standards_adherence_csv_export` feature flag

What does this MR do and why?

What

Remove compliance_standards_adherence_csv_export feature flag

• Removes compliance_standards_adherence_csv_export feature flag
• Updates docs to reflect global release

Why

Feature has been globally enabled and is stable

MR acceptance checklist

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

How to set up and validate locally

Setup Adherences

1. Visit group settings and enable "Prevent approval by author" from the 'Merge Request Approval' section.
2. This will create a couple of rows inside the project_compliance_standards_adherence table.

Using a group name visit the following below locally

http://gdk.test:3000/groups/-/security/compliance_standards_adherence_reports.csv

Related to #433421 (closed)