Cascade membership removal on organization user removal

What does this MR do and why?

Remove all of the user's group and project membership when removing them from an organization

References

• Resolves #629287 (closed)
• Discussion: https://gitlab.com/gitlab-org/gitlab/-/issues/622329

Screenshots or screen recordings

How to set up and validate locally

1. Enable the organization feature
2. Add a user to an organization in https://gdk.test:3443/o/<organization>/admin/users
3. Invite them as a member of a group in the organization
4. Remove them from the organization in https://gdk.test:3443/o/<organization>/admin/users

MR acceptance checklist

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