Why do you really need to delete them? Just let them go away with retention. While I understand the desire to "clean things up", please consider other use cases as well.
The reason why we don't provide this functionality is compliance. Ability to delete the history of user activity within the data management system makes the systems non-complaint with the related compliance requirements, policies and laws in most developed countries. Which, in turn, makes the product unusable for every customer who is the subject to those. Because now, anyone can restore a sensitive file from a file server backup, and immediately hide this activity.
Reading back through this page, we never had this capability in the user interface, and had purposely disabled the "workaround" that was unintentionally introduced as a part of our PowerShell API development. Obviously, we would not have disabled a feature that is already implemented and works fine without really serious reasons... we are not enemies to ourselves
