Remove unused claim from AI access token

What does this MR do and why?

• No longer used and not needed
• Also being removed from Gateway: gitlab-org/modelops/applied-ml/code-suggestions/ai-assist!450 (merged)
• More context: gitlab-org/modelops/applied-ml/code-suggestions/ai-assist#325 (comment 1638315123)

How to set up and validate locally

Removal of unused code.

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.