Resolve "`GET /api/:version/projects/:id/hooks` can be slow"

What does this MR do and why?

Based on the #364446, we are temporarily removing url_variables from the GET /hooks endpoint.

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Checkout the branch
2. Call the GET#hooks endpoint http://gdk.test:3000/api/v4/projects/project_id/hooks/
3. Validate that url_variables are not exposed

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 #364446