Properties are defined across all elements or services and removing one would remove it from all. And as far as I am aware there is no easy way to view/analyze the properties across all elements/services.
An option could be to use something like an automation script to navigate through all elements/services and analyze the ones being used.
In essence, you could retrieve all elements and build a list of all properties on the system.
You would then iterate over the elements and remove from the list any property that satisfies your condition of being in use (e.g. not being empty) and continue the process until you have analyzed all elements.
In the end, you should have a list of properties that are not used anywhere.