application: stop force disabling dark theme

https://bugzilla.gnome.org/show_bug.cgi?id=758057

src/gcal-application.c

@@ -246,8 +246,6 @@ gcal_application_activate (GApplication *application)
      if (error != NULL)
          g_warning ("Error loading stylesheet from file %s. %s", CSS_FILE, error->message);
 
-     g_object_set (gtk_settings_get_default (), "gtk-application-prefer-dark-theme", FALSE, NULL);
-
      g_object_unref (css_file);
    }