That's an informational message informing you that deleting logins does not delete the associated database users and to complete the delete you have to delete the database users yourself, potentially first transferring ownership of objects of schemas to other users.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
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We stand on the bridge and no one may pass