Update getting-started.rst

Comment didn't work so remove pre-installation link.

source/getting-started.rst

@@ -16,7 +16,6 @@ Follow the menu to the left and you will have a working PBX in no time.
   :maxdepth: 4
   :glob:
 
-..  getting-started/pre-installation.rst
   getting-started/installation-recommended.rst
   getting-started/post-installation.rst
   iptables.rst