There is a Default Security Rule called "OwnerPublishDuplicate". This Rule will enable all the app owners to publish the app, you can edit this rule and enable Delete option in this rule to enable App owners to Delete the App.
But before editing the default Security Rules please take a backup of the rule, later you can replace if you want.
Conditions: ((user.roles="cust_StreamAdmin")) and ((resource.name="Testing stream")) mean you can make specifed actions on resources which name is "Testing stream". But I assume none of your apps have that name , So that is not valid for the apps.
You can try like this:
Conditions: ((user.roles="cust_StreamAdmin")) and ((resource.type="Stream" and resource.name="Testing stream") or resource.type like "App*")