Remove the feature flag `ci_inbound_job_token_scope`

Waiting on the final commit in 15.9 final commit https://about.gitlab.com/handbook/engineering/releases/#how-can-i-determine-if-my-merge-request-will-make-it-into-the-monthly-release

What does this MR do and why?

Removes the feature flag to release the inbound job token scope feature.

Rollout issue: #376063 (closed)

Main feature issues:

• #346298 (closed)
• #375782 (closed)

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.