I think its not an option to delete but an option to select .. then delete. That would be in the "select by attributes" option.In there you can specify according to similarities of objects. Im not in my shop at the moment so i'm not 100% sure on that.
Actually, it is an option that removes tiny objects from a design/graphic when you specify a max size of the objects you would like to remove from a selection. Especially useful after vectorizing an object. You can find this tool on the Path edit tool bar. The icon is the next to last on the right. It depends on the version of Flexi that you are using. Lower versions may not have this function available.