styling: Don't switch app icons to symbolic for HC

While it's true that white against black has the ultimate contrast, the
  decision to switch fullcolor icons to symbolic has a few negative implications:

    * Apps identities usually lean onto colors, switching to white symbolic
      suddenly makes it harder to identify an app.
    * Many 3rd party apps don't ship a symbolic icon making the experience feel
      unpolished/"under construction".
    * Behavior is inconsistent with gtk/libadwaita.

Part of the HC polish initiative -- https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5799

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6136

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2555>

data/theme/gnome-shell-high-contrast.scss

@@ -5,11 +5,6 @@ $variant: 'dark';
 @import "gnome-shell-sass/_common";
 @import "gnome-shell-sass/_widgets";
 
-//force symbolic icons
-stage {
-	-st-icon-style: symbolic;
-}
-
 .toggle-switch { width: 48px; }
 .toggle-switch {
   background-image: url("resource:///org/gnome/shell/theme/toggle-off-hc.svg");