XmMultiListUnselectItem(3) on Linux
The text 7cf6267e7e0c, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
An MultiList function that deselects the specified item of the list "XmMultiListUnselectItem" "Extended List functions" "XmMultiListUnselectItem"