Agreed with @christianero1, setting up a smart campaign sounds like the apt choice for this. Also, FYR - list upload is used for importing/updating records in the DB (and cannot be used for removing people from the DB). You'd need to use the "Delete Person" flow step in the campaign flow; reference the list (smart/static) membership in the campaign's smart list criteria and since these people aren't synced over to SFDC, as a safety net you could also add the "SFDC Type is empty" filter to ensure that you're not letting any synced records to qualify.
You can also set a recurring schedule for this campaign, so it runs every week on its own (do this if you're sure that the people in the list are exactly the ones you'd want to remove permanently from the Marketo DB). Alternatively, you may also manually run this campaign on a weekly basis if you'd like to re-check the people qualifying for the campaign.
Campaign smart list (Add/Update filter logic, if required) -

Campaign Flow -
