The editor of a jounal asked me to withdraw the ArXiv version of a paper and only upload it after acceptance. Is it possible to do that?
I totally agree with the comments of @anyon and @david-ketcheson. I'd suggest that you 


point the editor to the guidelines regarding self-archiving of the journal and/or Elsevier in general and, if this fails, 
contact your library, because there are people dealing with this kind of situations very often and they usually have (other) contact persons/options at the publisher.