Cannot revoke super admin for non-existent user

[danielbachhuber]

Originally wp-cli/entity-command#31

Given a value for the site_admins site meta field which contains a username of a non-existent user, it's not possible to revoke this ghost super admin via WP-CLI.

The wp super-admin remove warns that the username you're attempting to revoke super admin access for is invalid, but then subsequently presents an incorrect success message:

$ wp super-admin remove admin
Warning: Invalid user ID, email or login: 'admin'
Success: Revoked super-admin capabilities.

In fact, the super-admin caps have not been revoked from the ghost admin user.