[gnome-control-center] power: Simplify cancellable destruction

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit ed6ac15b5ca8f567ccb71ab438f093f9c72c59a0
Author: Robert Ancell <robert ancell canonical com>
Date:   Thu May 31 09:20:53 2018 +1200

    power: Simplify cancellable destruction

 panels/power/cc-power-panel.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)
---
diff --git a/panels/power/cc-power-panel.c b/panels/power/cc-power-panel.c
index 98f1c26aa..34cfd9bed 100644
--- a/panels/power/cc-power-panel.c
+++ b/panels/power/cc-power-panel.c
@@ -128,12 +128,8 @@ cc_power_panel_dispose (GObject *object)
   g_clear_pointer (&self->chassis_type, g_free);
   g_clear_object (&self->gsd_settings);
   g_clear_object (&self->session_settings);
-  if (self->cancellable != NULL)
-    {
-      g_cancellable_cancel (self->cancellable);
-      g_object_unref (self->cancellable);
-      self->cancellable = NULL;
-    }
+  g_cancellable_cancel (self->cancellable);
+  g_clear_object (&self->cancellable);
   g_clear_pointer (&self->automatic_suspend_dialog, gtk_widget_destroy);
   g_clear_object (&self->builder);
   g_clear_object (&self->screen_proxy);