Remove FF for token removal

What does this MR do and why?

Related to #386871 (closed) and https://gitlab.com/gitlab-org/gitlab/-/issues/349877

It removes remove_job_token_on_completion FF which was enabled on .com on Feb 8.

Impact

It reduces the size of ci_builds by 175MB for each 1M processed builds, or by about 175GB per year.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

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.