recipient_row: Use a dimmed stream color for background.

Following important changes are being made here:
* color_class lib is removed since it not used anywhere now.
* We don't need the `dark_background` class since the background
  color is already adjusted based on color scheme. So, all
  instances of it being used is removed.

web/src/server_events_dispatch.js

@@ -689,6 +689,7 @@ export function dispatch_normal_event(event) {
                         realm_logo.render();
                     }
                     $("body").fadeIn(300);
+                    message_lists.update_recipient_bar_background_color();
                 }, 300);
             }
             if (event.property === "starred_message_counts") {