Remove unused method and add feature_category

What does this MR do and why?

Removes unused helped method ci_minutes_progress_bar and adds feature_category to ee/spec/helpers/ee/namespaces_helper_spec.rb.

Screenshots or screen recordings

No UI changes

How to set up and validate locally

bundle spec rspec ee/spec/helpers/ee/namespaces_helper_spec.rb should pass, and the pipeline job code coverage should be green.

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.