code: public void delete(String key)
  	{
  		String urlKey = urlEncode(key);
  		checkPreferenceKeyLength(urlKey);
  
  		osm.makeAuthenticatedRequest(USERPREFS + urlKey, "DELETE");
  	}
docs: Deletes the given preference key from the user preferences
  
  @param key preference to delete. Must be less than 256 characters.
  @throws OsmAuthorizationException if this application is not authorized to change the
  user's preferences. (Permission.CHANGE_PREFERENCES)