If you'd like to remove the Deliverability Audit workflow action from your HubSpot portal, please follow the below steps.
Navigate to the settings page in HubSpot by clicking on the gear icon in the top right. Underneath "Account Setup", you'll see a drop down for "Integrations" and then "Connected Apps". Navigate to "Connected Apps". You can then search for "Deliverability Audit" in the search bar. Once you have located the app, click on "Actions" and "Uninstall". This will uninstall the workflow action from your HubSpot portal entirely.
One thing to be aware of is if you have setup an automated workflow to update custom properties based on the deliverability audit tool (for example, using the field to track engagement rates in a HubSpot dashboard report), you'll want to turn the workflow off and delete it. Additionally, any dashboard reports that rely on this data will no longer work.