Remove "VM secure update mechanism (forthcoming)"

QubesOS/qubes-issues#3495

Author: Andrew David Wong

doc.md

@@ -245,7 +245,6 @@ Services
  * [Implementation of DisposableVMs](/doc/dvm-impl/)
  * [Article about disposable VMs](http://theinvisiblethings.blogspot.com/2010/06/disposable-vms.html)
  * [Dom0 secure update mechanism](/doc/dom0-secure-updates/)
- * VM secure update mechanism (forthcoming)
 
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