Remove current organization by user

What does this MR do and why?

Remove user organization as a possible input for the Current Organization isolation context.

References

The current organization inputs are listed at https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/organization/current_organization/ under the Web Requests heading.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #553146