Remove mentions of continuous_integration_scaling category

What does this MR do and why?

Continuous Integration Scaling category was removed via gitlab-com/www-gitlab-com!117369 (merged), but there's still one mention of it in the code.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.