Disable Contact Invoice Approval Workflow (InvoiceApprovalHumantask)

Summary:

How do we disable workflow emails for this task? We don't need any emails to go out since our business process is to approve them within the UI.

Content (required):

Workflow emails are being sent to individuals who are marked as principal investigators. We don't rely on this field other than it seems to trigger workflow emails to approve contract invoices.  We approve invoices from within the UI (centralized admin function) and don't require emails to be sent or approved.

How do we mark as processed all workflows that are currently showing as "in progress" which have been processed and completed via the UI.