window-list: Small stylesheet cleanup

The light stylesheet duplicates some declarations, and the
last occurrence matches what we already inherit from the
dark stylesheet.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/337>
(cherry picked from commit 860c56f83e)

extensions/window-list/stylesheet-light.css

@@ -21,21 +21,11 @@
     text-shadow: none;
   }
 
-  .bottom-panel .window-button > StWidget {
-    -st-natural-width: 18.7em;
-    max-width: 18.75em;
-  }
-
  .window-button > StWidget {
   color: #000;
   background-color: transparent;
 }
 
-.window-button > StWidget {
-  -st-natural-width: 18.75em;
-  max-width: 18.75em;
-}
-
 .window-button:hover > StWidget {
   background-color: st-darken(#eee,5%);
 }