The filedropper-widget has been deprecated for the new Mendix releases. That is probably the reason that it is now completely gone. Here is the link where it used to be, now giving you a nice 404.
You can still add it by copying the file from this project: https://github.com/mendixlabs/widget-test-projects/blob/master/projects/filedropper/FileDropper.mpk, though it will likely not get you the most recent version.
For information a new File Dropper module is now available in the marketplace. Have a look here:
https://marketplace.mendix.com/link/component/229507