Remove desktop files & binaries handling

Now that the desktop code is gone maybe we should remove the desktop files handling inside Nautilus (and with it maybe the ability to run binary files).

This started in the discussion about simplifying nautilus-link here:

Just to remember for posterity, iirc (and the code seems to go with this hypothesis) nautilus-link was an attemp to merge the functionality of special desktop links (like the home folder, hard drives and network icon) and other links and regular desktop files, so probably we can just remove this into a simpler handling in the future.

In any case, this issue should be used for its discussion since I personally have no idea of their use cases for the non-desktop case.