Hi there,
You can create a smart campaign to delete these people.
If all leads that are members of this program appeared on the list, you can use the Member of Program filter under the smart list tab. Under the flow step, drag Delete Person down to the stage. Here, you're able to tell Marketo if you want to delete these records from your CRM.

Running the Smart Campaign will delete these leads from Marketo.
Keep in mind that Salesforce will likely try sync these lead records back to Marketo if you're only deleting them from Marketo.
It always pays to keep a backup somewhere in case you have also accidentally deleted records you weren't intending to. I always recommend using caution and double, triple, quadruple checking everything when using this filter.