GraphQL: Remove Mutation.ciCdSettingsUpdate mutation

What does this MR do and why?

Describe in detail what your merge request does and why.

After we enabled the remove_cicd_settings_update FF on .com to make a sync release on the 22nd, this MR removed both the Mutation.ciCdSettingsUpdate mutation and the backing remove_cicd_settings_update FF.

Changelog: removed

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.