Try Project Manager.
There is a feature in PPRO to do exactly what you are asking. Its called Project Manager. With it you can save a trimmed version of your project to a new folder, where only clips used will be saved. Once done; archive that folder to some form of storage, then you can delete the original.
One little thing to check for, is that, depending on the Project folders' layout, a few Assets might not get gathered. SmartSound files can be in this category. Before you do the deletion, check that everything has been "trimmed" and copied correctly. Takes only a second, but could save you some extra work later on.