Please review Fig.1 and Fig.2 in the Synchronous mode and Asynchronous mode documentation sections respectively in this
article. They demonstrate the different way multiple uploaded files are displayed in both of the Upload's modes of operation. Since you are using synchronous mode the selected filenames are displayed as span elements within a single li element, i.e. there are no multiple uids but a single uid applied to a li element, within which all filenames are nested. There is no built-in functionality that allows the removal of separate filenames in this mode.
In async mode the Upload displays the uploaded files in a file list: each uploaded file is rendered in a separate li element (with class "k-file"). Each file in this mode has its own uid and can be removed separately.