theme: Don't dim text in backdropped list/listview

We have largely moved away from changing styles when :backdropped, aside
for some things in HeaderBars and Buttons. So we probably should not be
automatically dimming text in labels in list[view]s anymore either, as
that introduces differences if text happens to be in such widgets vs not

gtk/theme/Default/_common.scss

@@ -3271,7 +3271,6 @@ list {
   border-color: $borders_color;
 
   &:backdrop {
-    color: $backdrop_text_color;
     background-color: $backdrop_base_color;
     border-color: $backdrop_borders_color;
   }