Thought I had done something wrong as none of the javascript methods on an upload component, returning an 'xyz is not a function', however, having tried your own previews in your documentation, there is the exact same problem on your documentation page. So guessing this is not me...
Tried this out on chrome, IE & firefox on two different machines and the upload preview in your documentation fails on all of them.
http://docs.telerik.com/kendo-ui/api/javascript/ui/upload#methods-removeAllFiles
Dont really understand how this can happen in a 'stable' release...