[gnome-mahjongg] Do no mention a non-implemented shortcut.

[Arnaud B. <arnaudb src gnome org>]

commit b5134f4fafca423f0147109ffbc1c65504a8988a
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Fri Oct 9 16:18:59 2020 +0200

    Do no mention a non-implemented shortcut.

 data/help-overlay.ui | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/data/help-overlay.ui b/data/help-overlay.ui
index a14eef7..a81a848 100644
--- a/data/help-overlay.ui
+++ b/data/help-overlay.ui
@@ -40,9 +40,9 @@
             </child>
             <child>
               <object class="GtkShortcutsShortcut">
-                <property name="visible">1</property>
+                <property name="visible">0</property>
                 <property name="accelerator">F11</property>
-                <property name="title" translatable="yes" context="shortcut window">Fullscreen</property>
+                <property name="title" translatable="yes" context="shortcut window">Fullscreen</property> 
<!-- TODO implement? or not -->
               </object>
             </child>
             <child>