Hide instance-only elements from org admin users

What does this MR do and why?

Simplify the heading section of the organization users admin page. Removes the state card and buttons that are only suitable for the instance admin page.

References

Resolves #628413 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable ui_for_organizations and org_experimental feature flags
2. Visit /o/<organization_path>/admin/users.

MR acceptance checklist

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