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/extensionSystem.js

@@ -667,7 +667,7 @@ export class ExtensionManager extends Signals.EventEmitter {
             try {
                 FileUtils.recursivelyDeleteDir(extensionDir, false);
                 FileUtils.recursivelyMoveDir(dir, extensionDir);
-            } catch (e) {
+            } catch {
                 log(`Failed to install extension updates for ${uuid}`);
             } finally {
                 FileUtils.recursivelyDeleteDir(dir, true);