release_schedule: remove Zefram from release engineer backup list

RIP Zefram.

Author: mauke

Porting/release_schedule.pod

@@ -90,7 +90,6 @@ consent of the Steering Council.)
   Tatsuhiko Miyagawa <miyagawa@bulknews.net>
   Tony Cook <tony@develop-help.com>
   Yves Orton <demerphq@gmail.com>
-  Zefram <zefram@fysh.org>
   Ævar Arnfjörð Bjarmason <avar@cpan.org>
 
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