js: Remove unused catch bindings

Optional catch bindings have been supported for quite a while now,
so we can treat unused error bindings in catch statements like any
other unused variable.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3684>

js/ui/environment.js

@@ -348,7 +348,7 @@ Object.prototype.toString = function () {
             return base.replace(/\]$/, ` delegate for ${this.actor.toString().substring(1)}`);
         else
             return base;
-    } catch (e) {
+    } catch {
         return base;
     }
 };