Remove unused variable (#919)

dlib/gui_widgets/widgets.cpp

@@ -5628,9 +5628,6 @@ namespace dlib
 
         const unsigned long padding = style->get_padding(*mfont);
 
-        // find the delta between the cursor rect and the corner of the total rect 
-        point delta = point(cursor_rect.left(), cursor_rect.top()) - point(total_rect().left(), total_rect().top());
-
         // now scroll us so that we can see the current cursor 
         scroll_to_rect(centered_rect(cursor_rect, cursor_rect.width() + padding + 6, cursor_rect.height() + 1));