XmListDeleteItem man page
XmListDeleteItem — A List function that deletes an item from the list
#include <Xm/List.h> void XmListDeleteItem( Widget widget, XmString item);
XmListDeleteItem deletes the first item in the list that matches item. A warning message appears if the item does not exist.
Specifies the ID of the List from whose list an item is deleted.
Specifies the text of the item to be deleted from the list. If item appears more than once in the List, only the first occurrence is matched.
For a complete definition of List and its associated resources, see XmList(3).