It depends on what's inside the js (or coffee) files. So, if you never used the js file, meaning the file has the default text added by rails when the file was first generated, than yes, it's fine to delete. However, if you're including that file in other views because you have some custom code in that file than you should probably extract it elsewhere first.
Also please note, if you delete that file, make sure you're not rendering it in your controllers.