Remove ci_job_token_scope_enabled attribute from projects API endpoint

Proposal

We recently added API endpoints for job token scope. The /projects API endpoint still returns the attribute ci_job_token_scope_enabled. This is redundant and could have a minor effect on performance of that endpoint. We should remove that attribute.

Update 2025-05-30: Based on usage data we do not believe this is a breaking change as the only component using this was GitLab's frontend UI. Additionally the frontend component using this API has been removed in GitLab 18.0. I am removing the breaking change label.