I tried to delete one of them, but it won't go away.
Because each of them has different purpose. As @aneeshep suggested, you can see the real names of .desktop files using Terminal. Or go ahead and open those files in Gedit (drag&drop on Gedit's window).
You can remove them, but they'll be back at the latest with the next Evolution update, not to mention that Evolution will disappear from applications menu and you'll break desktop e-mail integration (like mailto: links support etc.).