Update AUTHORS

Removed Steve as main developer uppon his own request .
---------------------------------------------------------------------------------------------
Former Major Autors & coders ( not any more in the Project ) :

  Steve Kemp <steve [at] uk.org.steve>   - Noticed  Marc 2014 to support@remsnet.de 
     You should know that I no longer take part in any xen-tools development. 
     Instead the project was handed over to folks who had more time and energy to continue with it.
      
      Your contribution would be best shared with the mailing list here:

      http://xen-tools.org/mailman/listinfo/xen-tools-discuss